Atomic StructureANTHONY GATES

Today’s Objective

I can describe Dalton’s Atomic Theory.

I can explain the difference between subatomic particles.

Atoms

The smallest particle within an element that still retains its identity in a chemical reaction.

Early Ideas

Democritus: believed that the atom was indivisible and indestructible particles.His ideas were later challenged

Dalton used experimental methods to observe the patterns to which elements combined to form new products to turn Democritus’ ideas into scientific theory.

(John) Dalton’s Atomic Theory

1. All elements consist of tiny indestructible particles called atoms

2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element.

3. Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.

4. Chemical reactions occur when atoms are separated, joined or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.

Electrons

Discovered by J.J. ThomsonNegatively charged subatomic particlesLocated in the electron cloudWeighs 9.11 x 10-28 grams

So practically nothing

Symbol: e-

Proton

Discovered by Earnest Rutherford Positively charged subatomic particle Located in the nucleus Weighs 1.67 x 10-24 grams

So practically nothing… but still more than an electron.

1amu

Symbol: p+

Neutron

Discovered by James Chadwick Neutral (no charge) subatomic particle Located in the nucleus Weighs 1.67 x 10-24 grams

So practically nothing… but still more than an electron.

1amu

Symbol: n0

Recap

Dalton says what about the atom?1. Elements made up of tiny indestructible particles

2. Atoms are the same as atoms of the same element and different from atoms of different elements

3. Atoms of different elements can mix together or combine to create compounds of atoms in whole number ratios

4. Chemical reactions occur when atoms interact. Atoms cannot change into an atom of a different element.

Recap part dos

Three subatomic particles are…Electrons, protons, neutrons

Electrons are ________ charged.Protons are ________ charged.Neutrons are ________ charged.

Homework

Answer questions from your book:

Pg. 103 # 4, 5

Pg. 108 # 8, 10

Pg. 122 #34, 36, 37

Homework

Bellwork… do this as soon as you sit down

Draw a picture of what you believe an atom looks like.

Learning objectives

I can draw a model of the atom.

I can identify the number of protons, electrons and neutrons in an atom.

Thomson’s Model

Believed atom was a positively charged ball containing electrons

Commonly known as the Plum Pudding model

Earnest Rutherford’s Gold foil Experiment

Nucleus

Tiny central core of an atom and is composed of protons and neutrons.

Rutherford’s Model

Nucleus in the center containing protons and neutrons with a net positive charge

Electrons are evenly distributed around the nucleus taking up most of its volume.

Nucleus Size

If the nucleus was the size of a marble, then the atom would be about the size of a football stadium.

The nucleus contains a large majority of the atoms weight, but only a tiny amount of its size.

Assess for learning

Turn to a partner and describe what the Rutherford model of the atom looks like. Include words like:

nucleus, electrons, electron cloud, protons, and neutrons.

Inquiring minds want to know…

How do we distinguish between the elements? Elements are different because

they contain different amounts of protons.

The Atomic Number (insert booming voice)

Atomic number:The number of protons in a nucleus of an

atom of an elementEx. Hydrogen has one proton and thus its atomic

number is 1.Ex. Oxygen has eight protons and so its atomic

number is 8. This number will NEVER change for an element

Will that be cash or check? … Charge it baby!

An atom naturally has a neutral (zero) electrical charge

If the atomic number tells us the number of protons, which have a positive charge what does it also tell us about the electrons? The atomic number is also the number of electrons

The amount of electrons must equal the number of protons to have a neutral atom.

What about neutrons???

The atomic number will tell us how many electrons and protons there are, but how do we know how many neutrons there are?

Mass Number

Since the majority of the mass is in the nucleus as protons and neutrons, we can look at the weight to help us find the number of neutrons.

Because 1 proton or neutron weighs 1amu, the mass number will be directly related to the number of protons and neutrons.

Since helium has a atomic number of 2, it has 2 protons. If it has a mass number of 4amu, 2amu of the 4amu is the mass are because of the protons, but what about the other two? The other 2amu is the mass of the neutrons. 2amu 2 neutrons.

#Neutron

Number of Neutrons = Mass Number – Atomic Number

Chemical Symbols

Each element has its own chemical symbol. These are one or two letter combinations Examples

Oxygen: OHelium: HeGold: Au

Putting it all together… shorthand

Check for understanding

Phosphorus has an atomic number of 15 and a mass number of 31. Write out this information in shorthand and draw a Rutherford model of an atom for phosphorus.

Bellwork

Draw a Rutherford atom of Fluorine (F).

Learning Objectives

I can calculate the average atomic mass of a given set of isotopes.

Isotopes

Atoms that have the same number of protons, but a different number of neutrons. Because isotopes have different numbers of neutrons, they have different mass

numbers. Isotopes retain their chemical properties since the number of protons and

electrons have not changed. p+ and e- are responsible for chemical properties

Example

Hydrogen has one proton and no neutrons, thus giving it a mass number of 1. Hydrogen-1

An isotope of hydrogen has one proton and one neutron, thus

giving it a mass number of 2. Hydrogen-2

Atomic Masses

Because the mass of a single element is significantly small, they are impractical to work with.

It would instead be easier to use relative masses of atoms and select a reference isotope.

Carbon-12 was selected and 1/12 of the mass of a carbon-12 atom became what is now known as 1 atomic mass unit (amu)

Average Atomic Masses

A sample of almost any element contains a mixture of two or more isotopes.

Certain isotopes occur more often than others. The atomic mass is a weighted average mass of the atoms in a

naturally occurring sample of the element. The weighted average reflects both the mass and the abundance of

each isotope present

Calculating Atomic Mass

Carbon-12 makes up 98.89% of any sample of carbon, while carbon-13 makes up 1.11% of carbon.

Atomic mass of carbon= (12.00amu x .9889) + (13.00amu x .0111)

= 12.01amu

Quiz Practice!!

Draw the Rutherford and Plum Pudding models of Carbon-12.

Plum Pudding Model:

Rutherford Model of Carbon-12

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Quiz Practice

Element Symbol

Atomic Number

Mass Number

Electrons Protons Neutrons

Te 128

17 18

55 25

247 151

Quiz Practice

Element Symbol

Atomic Number

Mass Number

Electrons Protons Neutrons

Te 52 128 52 52 76

Cl 17 35 17 17 18

Mn 25 55 25 25 30

Cm 96 247 96 96 151

Quiz Practice

What is the average atomic mass of silicon if silicon-28 has an abundance of 92.21%, silicon-29 has an abundance of 4.70% and silicon 30 has an abundance of 3.09%?

Problems

Rutherford’s model could not explain chemical properties of elements. Examples:

Why some compounds give off certain colors when heated in a flame.

Why do some metals glow red, then yellow and even white as they are heated to higher temperatures.

Niels Bohr

Bohr proposed that electrons are found in only in specific circular paths, or orbits, around the nucleus

Each orbit around the nucleus has a fixed energy called energy levels.

Only works well for hydrogen atoms

Ladder Analogy

The farther up the ladder, the higher the energy level and less energy is needed to jump between levels.

Electrons can jump energy levels by gaining energy Quantum: the amount of energy required to

jump an energy level

You can’t stand between rungs

An electron doesn’t exist between energy levels

Bohr’s Model

In order to draw a Bohr model of an atom, simply draw the nucleus with a couple circles around it to symbolize the electron orbits.

Then draw in electrons on the orbits with only two on the most inner circle and up to eight on each of the other orbits.

Ex. Neon is shown to the right.

Practice drawing the Bohr model of carbon

Edwin Schrödinger

Devised a mathematical equation describing the behavior of an electron in a hydrogen atom.

Quantum Mechanical Model Determines the allowed energies an

electron can have and how likely it is to find the electron in various locations around the nucleus.

This is the currently accepted model.

Location by probability

Think of a propeller blade spinning around. It is difficult to locate it at any given moment, but to locate the region where the propeller is most likely to be located at any given moment is very easy.

Electrons move even faster than propeller blades and so determining their exact location is difficult, but determining the region they are most likely to be found is much easier.

Atomic Orbitals

Atomic orbitals: region in space where there is a high probability of finding an electron.

Homework:

Pg. 132# 1, 2, 3, 5, 6

Draw the Bohr model of the following elements:Hydrogen, Beryllium, Nitrogen and Fluorine

Quick Review of the Atom

https://www.youtube.com/watch?list=PLJicmE8fK0EiEzttYMD1zYkT-SmNf323z&v=xazQRcSCRaY&feature=player_detailpage

Review Bell Work

Grab a dry erase board and draw the Bohr model of an atom of Magnesium.

Think about which superhero is your favorite and why. Be prepared to share your answer.