You’re Officially Welcomed to VCE Chemistry 2015! By Miss Fitz Good news, everyone!

You’re Officially Welcomed to VCE Chemistry 2015!

By Miss Fitz

Good news, everyone!

How we will start the year…Unit 1, Area of Study 1

1.The historical development of the Periodic table

2.The historical development of The Atomic Structure

3.Mass numbers, isotopes and electron configurations

4.Trends of the periodic table5.Masses of particles6.The mole concept

1. The historical development of the Periodic table

The historical development of the Periodic table

(you learnt this stuff in transition… here’s a recap!)• The main guys…

Priestley and Lavoisier: In 1774, Priestley was the first to isolate elemental Oxygen, and Lavoisier discovered that Oxygen was the element that’s involved in combustion reactions.

Davy: This clever chap used electrolysis to isolate the elements potassium and sodium. He then discovered calcium, barium and strontium and was the first to produce elemental aluminium.

Dalton: Around the early 1800’s, Dalton used maths to prove that:All matter consisted of indivisible atomsAtoms of a particular element are identical in mass and have

identical properties.Atoms of each element have a unique mass.Atoms are neither created or destroyed in reactionsCompounds are formed from the combination of two or more

elements.

The historical development of the Periodic table

(you learnt this stuff in transition… here’s a recap!)

• The main guys… (continued)Berzelius: Assigned symbols to stand for the name of the elements. He also calculated accurately the relative atomic masses of many of the elements.

Mendeleev: The guy who created The Periodic Table!

Not sure if I should laugh at his beard or be impressed by it…

Dimitri Mendeleev…Mendeleev first arranged the elements in order of atomic mass and then examined the properties of the elements to discover that they changed periodically.

He arranged the elements with similar properties into vertical groups and elements in order of increasing atomic mass into horizontal periods.

Using the periodic trends and the chemical properties of elements, Mendeleev was able to accurately predict the appearance and properties of elements that had not yet been discovered.

Dimitri Mendeleev…






1.The historical development of the Periodic table √

2.The historical development of The Atomic Structure



2. The historical development of The Atomic Structure

The historical development of The Atomic Structure

(also covered in transition… here’s the recap!)

• Democritus: around 400BC

Democritus was the first scientist to create a model of the atom. He was the first one to discover that all matter is made up of invisible particles called atoms. He created the name "atom" from the Greek word "atomos", which means uncuttable. He also discovered that atoms are solid, insdestructable, and unique. Democritus didn't know about the different elements, or about a nucleus or electrons, all he knew was that everything is made of atoms. Leaf

atom



• Dalton: 1808John Dalton was an English chemist that created the Atomic Theory of Matter, a composition of previous findings by Democritus and his own findings. He included in this theory that all matter is made of atoms, that atoms cannot be created nor destroyed and also, atoms of different elements combine in whole ratios to form chemical compunds. His theory would later contribute to an advance in the atomic model.

Carbon atom



• Sir JJ Thompson: 1897J.J. Thomson was a very important scientist when it came to the atomic model. Up until his time, all models of the atom looked like a big solild ball. J.J. Thomson discovered the electron, which led him to create the "plum pudding" atomic model. In this model, he thought that the atom was mostly positive, and negative electrons wandered around the atom. The "plum pudding" model influenced other scientists to make better atomic models.



• Lord Rutherford: 1911Ernest Rutherford was another scientist that changed the atomic model. He found that J.J. Thomson's model was incorrect, so he created a new one. He created the nucleus, and said that instead of the positive matter being the whole atom, it was just in the middle. He said the atom was mostly empty space and that the electrons surrounded the positive nucleus. This model influenced one of his own students to perfect the atomic model later on.



• Neils Bohr: 1913Niels Bohr was a Danish scientist that was a student of Rutherford. He decided to make a new model based off of Rutherford's model, but changed the orbit of the electron. Also, he created energy levels in the atom, where only a certain amount of electrons could fit on one energy level of the atom. Bohr also used Planck's ideas in order to create quantum mechanics, his new concept regarding energy. This model is still used to this day.

It’s not

really

boring!



• Schrdinger/Plank/Heisenberg 1900-1927Erwin Scrhodinger was an Austrian scientist that worked with the Quantum model of the atom. He disagreed with Bohr's theory, so he created his own. He thought that the only way to find the location and energy of an electron in an atom was to calculate its probability of being a certain distance from the nucleus. This equation influenced the Quantum mechanical model of the atom.

Max Planck developed his ‘Quantum theory’, which states that energy exists in fixed amounts called quanta.

Werner Heisenberg was a German scientist that proposed the uncertainties of the Quantum model. He said that you can't know the exact velocity and momentum of the electron at the same time, which means you can't know the exact location of the electron. This principle proves error in Bohr's model because of the uncertainty of the location of an electron.



• Sir James Chadwick:1932

James Chadwick was an English scientist that discovered the neutron. Before this discovery, Rutherford had concluded that the nucleus was made of positive matter. It made sense that the atom was neutral because the negative electrons and the positive protons cancelled out. But, Chadwick started to question why there was a difference between the atomic mass and the number of protons. Chadwick then found that the missing component was a neutral part: the neutron.



• The Current model:

You’re invited!!!

• When: Chemistry class• Where: A8 – our knowledge inspiring

laboratory• What to bring: Any item of food that

can be shared that you feel is representative of any one of the models of the Atomic Theory.

Write this in your diary!

Atomic Theory PartyYou are invited to celebrate the superb discoveries and the contributions made by many learned Legendary Scientists!


1.The historical development of the Periodic table√

2.The historical development of The Atomic Structure√



3. Mass numbers, isotopes and electron configurations


(the recap continues…)

Subatomic ParticlesAtoms are composed of three subatomic particles: protons, neutrons and electrons. The two important properties of these particles are mass and charge:

The mass of electrons is negligible when compared to the mass of protons and neutrons, so their mass is not included when calculating the mass of the atom.

Particle

electron

neutron

proton

Relative charge

Relativemass

-11/1840

01

+11



The mass number of an atom is the number of protons plus the number of neutrons, and is represented by the symbol A.

When an atom is represented by its symbol, the mass number, and sometimes the atomic number, are shown.

The number of protons in an atom is known as the atomic number or proton number and is represented by the symbol Z.

mass number (A)

atomic number (Z)



atomic number is the same

mass number is different

The reactivity of different isotopes of an element is identical because they have the same number of electrons.

Isotopes are atoms of the same element that contain different numbers of neutrons.

The different masses of the atoms means that physical properties of isotopes are slightly different.

carbon-12 carbon-13



electron configurationIn year 10, you learnt the model of the atom states that a nucleus is surrounded by shells of electrons. Each shell holds a different maximum number of electrons:

At VCE, this model is slightly different. Instead of electrons being arranged in shells that are a different distance from the nucleus, they are arranged in energy levels.It was found that there are actually sub-levels to the shells you have previously learnt about.

1st shell : 2 electrons 2nd shell : 8 electrons 3rd shell : 8 electrons.

electron configurationThere are four sub-levels (sub-shells), labelled in order of increasing energy: s, p, d and f. Each holds a different number of electrons.

max no. electronssub-level

sub-levels max no.electrons

principal energylevel, nEach

principal energy level (shell) contains a different number of sub-levels.

14f

10d

6p

2s

4s, 4p, 4d, 4f

3s, 3p, 3d

2s, 2p

1s

324

183

82

21

electron configuration


electron configurationAs part of his work on electron configuration, Niels Bohr developed the Aufbau principle, which states how electrons occupy sub-levels.

The Aufbau principle states that thelowest energy sub-levels are occupied first.

This means the 1s sub-level is filled first, followed by 2s, 2p, 3s and 3p.However, the 4s sub-level is lower in energy than the 3d, so this will fill first.



electron configurationAlthough the 3d sub-level is in a lower principal energy level than the 4s sub-level, it is actually higher in energy.

Example: what is the electron structure of vanadium?

231. Count number of electrons in atom

1s22s22p63s23p64s23d32. Fill sub-levels, remembering 4s is filled before 3d

This means that the 4s sub-level is filled before the 3d sub-level.


electron configuration of ions

When an atom loses or gains electrons it produces a charged particle called an ion.

An ion that has gained electrons forms a negative ion.

An ion that has lost electrons forms a positive ion.

That’s because electrons are

negatively charged!

electron configuration of ionsWhen writing the electron

configuration of ions, it is important to add or subtract the appropriate number of electrons.

For negative ions add electrons.

Example: what is the electron structure of O2-?


1s22s22p63. Fill sub-levels as for uncharged atom

8 + 2 = 102. Add or remove electrons due to charge

For positive ions remove electrons.

For non-transition metals, the sub-levels are then filled as for atoms.

electron configurationsWhen transition metals form ions, it is the 4s electrons that are removed before the 3d electrons.

Example: what is the electron structure of Ni2+?


1s22s22p63s23p64s23d82. Fill sub-levels, remembering 4s is filled before 3d

1s22s22p63s23p63d84. Remove electrons starting with 4s

23. Count number of electrons to be removed

electron configurations

Valence electronsThe electrons in the outermost shell of an atom are called the valence electrons.

The valence electrons have the lowest ionisation energy (require the lowest energy to remove) and are responsible for most chemical reactions.

Chemists can usually predict the nature of an element by knowing the number of valence electrons.

Eg: Sodium has 1 valence electron.Eg: Chlorine has 7 valence electrons.




3.Mass numbers, isotopes and electron configurations√


4. Trends of the periodic table

Trends of the periodic table

The electronic arrangement of an atom made it possible to see why element properties are periodic.

The alkali metals in the first group of the Periodic Table all have outer shell electron configurations of s1.

The halogens all have outer shell electron configurations of s2p5.

Mendeleev’s periodic law can be restated as:

Periodic variations in the chemical properties of elements arise from periodic variations in the

electronic structures their atoms.

Trends of the periodic tableSo, How is it organised?

The genius of the periodic table is that it is organized like a big grid. The elements are placed in specific places because of the way they look and act. If you look at a grid, you know that there are rows and columns. The periodic table has rows and columns, too, and they each mean something different.


Rows are called Periods

Even though they skip some squares in between, all of the rows go left to right. When you look at a periodic table, each of the rows is considered to be a different period (Get it? Like PERIODic table.)

Trends of the periodic tableRows = periods

In the periodic table, elements have something in common if they are in the same row.

All of the elements in a period have the same number of atomic orbitals (shells).

Every element in the top row (the first period) has one shell for its electrons. All of the elements in the second row (the second period) have two shells for their electrons. It goes down the periodic table like that.

That’s why the top row only has Hydrogen (1s1) and Helium (1s2) – The first shell can only hold two electrons.

Trends of the periodic tableAnd then, there are groups…

The periodic table has a special name for its columns, too. When a column goes from top to bottom, it's called a group.

Trends of the periodic tablecolumns = groups

The elements in a group have the same number of electrons in their outer orbital.

Every element in the first column (group one) has one electron in its outer shell. Every element on the second column (group two) has two electrons in the outer shell. As you keep counting the columns, you'll know how many electrons are in the outer shell.

There are some exceptions to the order when you look at the transition elements, but you get the general idea.

Trends of the periodic tableblocks of elements

The Periodic Table can be divided into four main blocks of elements.

The s-block contains the Group I and II elements. These elements have s1 or s2 subshells as their highest energy subshells.

The p-block contains the Group III-VIII elements. These elements have outer shell configurations of s2p1 to s2p6.The elements in s- and p-block are sometimes referred to as main group elements.


The d-block contains elements known as the transition metals. It contains elements in which the 5 orbitals of the d-subshell are being progressively filled.

The f-block contains the lanthanides and the actinides.

The lanthanides contain elements where the 4f-subshells are being filled.The actinides contain elements where the 5f-subshell is being filled.



S


S P


S PD


S PD

F


TREND EXPLANATIONAtomic RadiusINCREASES Down a Group

Electrons occupy most of the volume of the atom.

Atomic Radius DECREASES across a period

The size of atoms decreases due to the increasing positive charge of the nucleus. This greater core charge pulls the electrons closer causing the volume of an atom to reduce.

Trends of the periodic tableTREND EXPLANATION

First Ionisation Energy DECREASES down a group

Atoms become larger due to more shells and the outer electrons are further from the nucleus feeling less core charge. The energy required to remove these outer shell electron decreases.

First Ionisation Energy INCREASES across a period

As the strength of attraction between the outer electrons and the nucleus increases, the energy required to remove the outermost electron increases as they feel more core charge.


TREND EXPLANATIONElectronegativityDECREASES Down a Group

As the outer electrons become more distant, electrons feel less core charge so have a weaker attraction to the nucleus.

ElectronegativityINCREASES across a period

The electron attracting ability of atoms increases as the pull on the outer electrons increases.


Trends of the periodic tablepatterns in groups

Even though elements in the same group have very similar properties there are some major differences as you move down the group.

Some of the following trends are noticeable as you move down a Group:

• The size of the atom increases• The first ionisation energy decreases• The atom becomes more metallic• Reducing strength of metals increases• Oxidising strength of non-metals decreases• Electronegativity decreases

Trends of the periodic tablepatterns in periods

As you move across the period, not only does the number of outer shell electrons increase but the number of protons increases which increases the core charge within the nucleus.

Due to this reason, as you move across a period:

The size of the atom decreasesFirst ionisation energy increasesElements become non-metallicReducing strength decreasesOxidising strength increasesElectronegativity increases



The periodic tableGroup 1








The periodic tabletransition metals

The periodic tablelanthanides

The periodic tableactinides

The periodic tabletransactinides





4.Trends of the periodic table√5.Masses of particles6.The mole concept

5. Masses of particles

Masses of particlesThe relative isotopic mass of an atom is its mass compared to the isotope carbon 12 (12C – a carbon atom with 6 protons and 6 neutrons).

12C is said to have a mass of exactly 12 units. All other masses are relative to this.

Relative atomic mass –Why does the periodic table have decimal numbers for the mass numbers?Most elements have more than one isotope. The

relative atomic mass of the element is the average mass of the isotopes taking into account the abundance of each isotope.

Example: what is the Ar of boron?

In a sample of boron, 20% of the atoms are 10Br and 80% are 11Br.

If there are 100 atoms, then 20 atoms would be 10Br and 80 atoms would be 11Br.

The relative atomic mass is calculated as follows:

Ar of Br = (20 × 10) + (80 × 11)100

Ar of Br = 10.8

Masses of particlesrelative atomic mass

100

)%(

abundanceotopicmassrelativeisAr

To calculate the relative atomic mass use:

Example 1: Calculate the relative atomic mass of chlorine.

Masses of particles

Masses of particles

Example 2:The relative atomic mass of copper is

63.54. If copper has two isotopes, 63Cu with a relative isotopic mass of 62.95 and 65Cu with a relative isotopic mass of 64.95, calculate the percentage abundance of the isotopes.

Masses of particlesrelative molecular mass

The relative molecular mass (Mr) is the sum of all the relative atomic masses (Ar) of each atom present in a molecule.

Eg: Oxygen:Atomic Mass = 16 (From periodic table)Molecular Mass = Add all the atomic masses together.

Mr (O2) = 2 X 16

= 32

We multiply by 2 because there a two oxygen atoms in the molecule

Masses of particlesrelative molecular mass

If you have an iPad or iPod you might want to get this app to make calculating molecular mass quicker (there is also an android version)…

ChemCalc





4.Trends of the periodic table√5.Masses of particles√6.The mole concept

6. The mole concept

The mole concept

The mole concept

Because every atom has a different atomic mass, it is difficult to be consistent when comparing the weights of different substances.

Chemists find it easier to deal with the number of particles of the substance.

The standard amount of particles is known as a mole

The mole concept

1 mole contains the same amount of particles contained in exactly 12g of 12C.

The number of particles in 1 mole of any substance is 6.02 1023.

This amount is known as Avogadro's Constant (NA).

The mole conceptWhen calculating the amount of a substance we use the formula:

Where:

n is the amount of the substance in moles

N is the number of particles present

NA is Avogadro’s constant

The mole conceptmolar mass

The Molar Mass (M) of a substance is the mass of 1 mole of that substance.

Since 1 mole of 12C is exactly 12g, the molar mass of an element is the same as its relative atomic mass.

Given that molar masses vary greatly between substances, masses of one mole of different substances can also vary greatly.

The mole conceptmolar mass

Figure 4.10 The equivalent of one mole of some common elements and compounds.

The mole conceptcounting by weighing

Using the molar mass we can calculate the amount of a substance if we know the mass. This is done by using the formula:

Mr

mnWhere:

n is the amount in moles

m is the mass in grams

Mr is the Molar Mass

The mole conceptformulas of compounds

• Using molar masses we can calculate the percentage composition of each of each element within a compound.

• This can be calculated by:100

____

_____%

compoundofmassmolartotal

compoundinelementofmassmolarncompositio

The mole conceptfinding the composition of a compound

Using chemical analysis we can find the simplest whole number ratio of atoms in a compound.

This is called the empirical formula.

Empirical formulas are determined experimentally, usually by finding the mass of each element in a given compound.

The mole conceptempirical formula

Calculating the empirical formula:

Measure the mass of each element in the compound

Calculate the amount in mole of each element in the compound

Calculate the simplest whole number ratio of moles of each element in the compound

Empirical formula of the compound

The mole conceptempirical formula

Example 1A compound of carbon and oxygen is found to contain 27.3% carbon and 72.7% oxygen. Calculate the empirical formula of the compound.

Example 29.0g of a compound of carbon, hydrogen and oxygen is found to contain 4.8g of oxygen and 3.6g of carbon. Calculate the empirical formula of the compound.

The mole conceptmolecular formula

The molecular formula of a compound gives the actual number of atoms present in a molecule of a compound.

For example, the empirical formula of glucose is CH2O. Its molecular formula is 6 times larger – C6H12O6.

A molecular formula can be deduced from the empirical formula of a compound if the molar mass is known.

The mole conceptmolecular formula

ExampleA sample of a hydrocarbon was found to contain 7.2g of carbon and 1.5g of hydrogen. The molar mass of the compound is 58. What is the molecular formula of the compound?





4.Trends of the periodic table√5.Masses of particles√6.The mole concept√

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