Chemical Reactions

Year 10 Science

Using this PowerPoint• This is a close copy of the PowerPoint I use in class. Normally I am

explaining and taking questions as we go, so you may find some gaps in your understanding. Use the forum to ask questions and I’ll do what I can to answer them.

• As you work through the PowerPoint you will come to pages with a in the top left corner of the page, this is to remind you that you have work to do; sometimes some exercise or worksheet, sometimes work from you Success in Science homework book.A is a page you may want a copy of for your notes. You will find the file in the printing files sectionA question in blue script is something I would ask the class, have a think see, if you can answer.

• Remember I would much rather you print off the notes from the PowerPoint and spent time learning the material (highlighting, underlining or what ever you like to do to help understand and remember the material) than spent twice as long coping and not really learning the work.

Work wellMK

What’s in This unit?

We’ll look at;• The different types of atoms• The periodic table• How atoms react with one anotherYou’ll learn to;• Write the names and symbols of the first 20

elements and 10 others• Recognise the signs of chemical reactions• Balance compound formulae

Some of this you will have covered in Year 9, so this will be revision

What are Chemicals made of?

Chemicals are made of tiny particles called atoms

Atoms are;• so small that they can’t be seen even by

the most powerful microscope• different -there are 92 (naturally

occurring) types of atom or elements (see the periodic table)

Groups of Atoms

• Atoms are often found in groups;– When all the atoms are the same type they

are called an element. – When there are different types of atoms that

are joined together by chemical bonds they are called a compound

– When there are different kinds of atoms that are together, but not joined by chemical bonds they are called a mixture

Mendeleev and the Periodic Table

• Mendeleev was a Russian scientist who was born in 1835 in Tobolsk, western Siberia.

• At this time there were only 63 elements (types of atoms) known.

• Many scientists were trying to organise them into some sort of order.

• Mendeleev came up with a table (- the Periodic Table) that ordered the elements in rows according to their number of protons and in columns according to their electron arrangement.

• He even left gaps for elements that hadn’t been discovered.

Periodic Table

• Fill in your blank periodic table with the first 20 elements using slide 8(make sure you include the name, symbol, and both numbers in each blank box)

• Also find and add iron, zinc, gold, silver, copper, mercury, selenium, tin, lead and iodine

Memorising the Elements

• It is important that you have memorised the first twenty elements (names and symbols) and the 10 others you have copied onto your periodic table.

• If you’re not sure if you know them take the element quiz

• If you don’t do well on the quiz use the learning elements in 4 nights sheet to help you

Have a listen to this crazy guy, he knows them all

So what about atoms?

Last year you will have looked at atoms and their structure

What do you remember?

What are atoms made of?How are the different types of

atoms different?

Second Electron Shell

(max. 8 electrons)

The Structure of The Atom

-

The Nucleus

Protons (+ve charge)

Neutrons (no charge)

+ ++

-

-

Electrons (-ve charge)

First electron shell (max. 2 electrons)

The Parts of an Atom

• There are three smaller particles that make up atoms– Protons -found in the nucleus and have a positive charge– Neutrons – found in the nucleus and have no charge

(neutral)– Electrons –found in orbit around the nucleus, smaller and

negatively charged

Particle Location Charge Mass

Proton NucleusPositive (+ve)

1

Neutron NucleusNo charge (neutral)

1

Electron OrbitalNegative (-ve)

1/1850

The Periodic Table•The periodic table contains the names and chemical symbols of all the 103 different types of atoms

•It also all the information about the structure of each atom.

Mass Number

–the number of protons plus

neutrons in the nucleus

3

7Li

Element symbol

Atomic Number

-the number of protons

Lets do a few

Write down the chemical symbol, atomic number and mass number for;

carbon

fluorine

magnesium

silver

tin

Atomic Number (symbol Z)

Mass Number (symbol A)

++ +

+

++

++

– the number of protons in the nucleus

– the number of nucleons (protons and neutrons) in the nucleus.

So what was that again?

4

9Be

Second Electron Shell

(max. 8 electrons)

The Structure of The Atom3

7Li

-

The Nucleus

Protons (+ve charge)

Neutrons (no charge)

+ ++

-

-

Electrons (-ve charge)

First electron shell (max. 2 electrons)

Lets look at Lithium or

It has Protons Neutrons Electrons

Li7

3

3 4 3

Lets draw some

Try•helium•Beryllium•Carbon•Magnesium

Atomic Number (Z) and the Periodic Table

• The atomic number (Z) is what makes each element unique (they all have a different number of protons)

• Elements are arranged on the periodic table in order of their atomic number (Z)

Patterns in the Periodic table

There are other patterns in the periodic table

• Complete the worksheet by drawing the elements in three of the groups (columns) of the periodic table and look for a pattern.

• Choose your elements from groups 1 and 17 or 2 and 16

• The worksheet is called; Patterns in the Periodic Table

Patterns

• Group 1 all have one lone electron in their outer electron shell

• Group 2 all have only two electrons in their outer electron shell

• Group 16 all have two electrons missing from their outer

electron shell

• Group 17 all have one electron missing from their outer

electron shell

• Group 18 all have full outer electron shells (this is the most

stable configuration and means group 18 elements are

unreactive)

Chemical Reactions and Physical Change

Chemical change (reaction) – involves the making or breaking of

chemical bonds, they are usually not easily reversible

Physical change– Involves a change in the physical nature

of a chemical, but not change in bonding, these changes are usually easily reversed

Practicals

There are a series of practicals that we do in class if you have missed these you will need to catch up with one of your class mates and get a copy of their observations and results

The Signs of Chemical Reactions

1. New substances formed2. Original substance used up3. Colour change4. Heat and/or light given off5. Gas produced (bubbling)

If you observe two or more of these signs you have a chemical reaction

Chemical Bonds

Compounds form when two or more atoms bond together

Chemical bonds are formed when atoms give or receive electrons (Ionic bonds) or share them (Covalent bonds)

Metals and Non-metals• Elements of the periodic table a grouped into two types

metals and non-metals. These types have different properties and characteristics.Turn to the periodic table you filled in and add the staircase like boundary between metals (brown) and non metals (light blue) (see the black line on the periodic table below)

Ionic and Covalent Bonds

• Ionic Bonds – Formed when a metal and a non-metal react to

form a compound– Involve electrons being given and received

e.g.

• Covalent Bonds– Formed between non-metals– Electrons are shared between atoms

e.g.

Ions

• When atoms lose or gain electrons (valency electrons) they become charged and are called ions

– Atoms that lose electrons form positive ions H+, Ca+2

– Atoms that gain electrons form negative ions Cl-, O-2

• Positive and negative ions are attracted to each other and form compounds

Let’s look at BerylliumAtom

p= 4n= 5e= 4

Ion

p= 4n= 5e= 2

49Be

-e

-e

-e-e

-e

-e

49Be

Be 2BeThe beryllium atom is electrically neutral as the positive protons are neutralised by the negative electrons

The beryllium ion has a charge of +2 as there are two more protons than electrons

The ion loses two electrons to become more stable with a full outer shell

Let’s look at OxygenAtom

p= 8n= 8e= 8

Ion

p= 8n= 8e= 10

816O

-e

-e

-e

-e

-e

-e

816O

O -2OThe oxygen atom is electrically neutral as the positive protons are neutralised by the negative electrons

The oxide ion has a charge of +2 as there are two more protons than electrons

The ion gains two electrons to become more stable with a full outer shell

-e

-e

-e-e

-e

-e-e

-e-e

-e

-e-e

-e

-e

-e

-e

-e

-e

-e

-e

Getting it together; Beryllium oxide

2Be -2O

-e

-e

-e-e

BeO

Because these ions have opposite charges there is

a strong attraction between them this is an

IONIC BOND

Be O

File is called; Patterns in the Periodic Table

Ion Names

• Ions often have a slightly different name from the atom

Atom name Ion name

oxygen (O) oxide

fluorine (F) fluoride

chlorine (Cl) chloride

sulfur (S) sulfide

iodine (I) iodide

Ions from the Periodic Table

Atom name

Ion name

Electrons to

lose/gain

Counts p e

Ion Charge

PotassiumPotassium

1 lose 19 1919 18 +1

Calcium 2 lose 20 2020 18 +2

ChlorineChloride

1 gain 17 1717 18 -1

Oxygen 2 gain 8 8 8 8 -2

Table of Ions+1 +2 +3 -2 -1

H+ hydrogen Cu2+ Copper Fe3+ Iron (III) O2- oxide Cl- chloride

Na+ sodium Fe2+ Iron (II) Al3+ Aluminium S2- sulfide F- fluoride

K+ Potassium Ca2+ Calcium SO42- sulphate I- iodide

Li+ Lithium Zn2+ Zinc CO32- carbonate OH- hydroxide

NH4+ Ammonium Mg2+ Magnesium

HCO3- hydrogen

carbonate (bicarbonate)

Pb2+ Lead NO3- nitrate

Notice that;

1.Some atoms change their name slightly when they become an ion

2.There are some unusual ions as you copied your ion table –they are polyatomic ions

What do you think polyatomic means?

Compound Names and Formulae

• Each compound has a unique name and formula that describe the make-up of the compound

• Both names and formulae are a combination of the atoms that make up the compound

Try these….

File called;Naming and Writing Compounds

Balancing Compound Formulae

• Always keep in mind that compounds are formed when atoms have gained or lost electrons –bonding is about electronsHave you noticed that so far we have looked at compounds formed between groups 1 and 17 and groups 2 and 16

• To write formulae for compounds with different valences (charges) we need to balance the formulae to make sure the number of electrons gained is the same as the number given (lost)

So how….?• Lithium oxideLi+ and O2- to balance the charges we need two Li+

so Li2SO4

• Copper chlorideCu2+ and Cl- to balance charges we need 2 Cl-

so CuCl2

Use small subscript numbers after symbol to show the number needed to balance the

electrons

Try these….

• Sodium oxide

• Potassium sulfide

• Calcium fluoride

• Magnesium chloride

• Sodium carbonate

• Hydrogen sulphate

• Na2O

• K2S

• CaF2

• MgCl2

• Na2CO3

• H2SO4

….and these tricky ones!!

• Calcium hydroxide

• Magnesium nitrate

• Ammonium sulphate

• Ca(OH)2

• Mg(NO3)2

• (NH4)2SO4

Polyatomic Ions

• Polyatomic ions are ions formed from 2 or more different elements (they all have 2 or more chemical symbols)

• They stick together and behave as if they are one single ion

• The subscipt numbers indicate the number of atoms of the element before the number

i.e. NO3 is made of 1 nitrogen ion and 3 oxygen ions

Try these….

For each polyatomic ion, fill in the gaps in the table

Ion Name Ion Formula Element count Valency (Charge)

OH- O=1, H=1 -1

nitrate NO3-

HCO3-

S=1, O=4

ammonium

NH4+

File called; Breaking Down Polyatomic ions

Polyatomic Ions in Formulae• When using polyatomic ions in formulae

brackets must be used if there are more than one of the polyatomic ion;

But not for

or

2-2 Ca(OH) OH Ca

23-3

2 )Mg(NO NO Mg

33 KNO NO K

3223 COLiLi CO

Balancing Formulae Practice

•Work your way through these examples and see if you can balance the formulae

File called; Balancing Compound Formulae

How well do you Understand?

• How many different kinds of atom make up the following compounds?

HClH2SO4

NaHCO3

• Now count the number of atoms that make up these compounds

Worksheet