8F Compounds and Mixtures - science

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Exam tip; A symbol represents 1 atom of an element

Some new symbols to get used to…

GCSE Core Chemistry


Key words; Atom, Compound, Electron, Element, Symbol

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H H

How do you know?



Learning Objectives

By the end of the lesson I can:

•Describe how elements contain only one type of atom

•Understand that symbols are used for atoms to show what happens in chemical reactions.

•Know that all 100 known elements are listed on the periodic table and groups have similar properties


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Atoms and symbols

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Elements are substances that each contain only are represented by a symbol.

Examples of symbols used for elements are O



More work on symbols

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Fill in the gaps in the table below.

Name of element

Chlorine

Carbon

Silver

Bromine

Sodium

Symbol

Cl

C

Ag

Br

Na



How are the elements arranged?

Answer: Using the Periodic Table

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Vertical columns are called horizontal rows are called



Elements, mixtures and compounds

Elements – these are substances containing

1 of 20 an element and is made up of sodium atoms only.

Compounds – these are substances made up of two or more types of atom. These atoms are joined together chemically. For example, carbon dioxide contains carbon and oxygen atoms joined together by chemical bonds.


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Mixtures –

these are not pure substances. The compounds and/or elements making them up are not joined chemically. For example, air is a mixture of gases like oxygen (an element) and carbon dioxide (a compound).



Elements, mixtures and compounds, continued

Classify the following substances as elements, mixtures or compounds.

1 of 20 mixture compound element





•Describe how elements contain only one type of atom


•Know that all 100 known elements are listed on the periodic table and groups have similar properties


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Key words; Atom, Compound, Electron, Element, Symbol

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•Know that atoms bond and rearrange in a chemical reaction


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A compound is made when atoms of different elements react and join together.

For example, water is produced from the chemical reaction between hydrogen and oxygen.

hydrogen + oxygen water

H H

+ O O

H H

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Two hydrogen molecules react with one oxygen molecule to produce two molecules of water.

Why does water have different properties to its elements?



A compound has different properties to the elements from which it is made because the atoms are joined differently.

carbon + oxygen carbon dioxide

+

Black solid used as fuel.

Colourless gas in which many substances burn.

Colourless gas used in fizzy drinks and fire extinguishers.

C + O O


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A compound is not a mixture

The atoms in a mixture of hydrogen gas and oxygen gas, which have not reacted with each other, look like this…

The atoms in water, the compound made when hydrogen and oxygen react and their atoms become chemically joined to each other, look like this…



To name simple compounds of metals and non-metals:

1.

Write down the name of the metal.

2.

Write down the name of the non-metal, changing the ending of the word to “ide ”.

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What is the name of the compound made when the following elements combine?

 magnesium and oxygen

 sodium and chlorine

 oxygen and iron magnesium oxide sodium chloride iron oxide



How do we name compounds?

The rules are:

1. If there are two elements present, then the name ends in –IDE.

For example, the formula CuS represents the compound _________ ide.

2. If there are three elements present and the third one is oxygen, then the name ends in – ATE .

For example, the formula CuSO

4 represents _________ate.


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What is the name of each compound formed by these metal and non-metal elements?

Element 1 Element 2 Name of compound iron magnesium sodium tin aluminium nickel zinc lithium sulphur nitrogen chlorine oxygen bromine iodine sulphur nitrogen iron sulphide magnesium nitride sodium chloride tin oxide aluminium bromide nickel iodide zinc sulphide lithium nitride


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Many compounds contain more than two elements.

For compounds containing two elements plus oxygen, the ending of the other nonmetal usually changes to “ -ate ”.

Element 1 Element 2 nickel sulphur magnesium nitrogen sodium copper aluminium nitrogen sulphur bromine

Element 3 oxygen oxygen oxygen oxygen oxygen

Name of compound nickel sulphate magnesium nitrate sodium nitrate copper sulphate aluminium bromate



Naming compounds, continued

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Name the compounds in the table below.

Formula

AlCl

3

CuO

Fe

2

O

3

CaSO

4

CaCO

3

MgBr

2

NaNO

3

Name

Aluminium chloride

Copper oxide

Iron oxide

Calcium sulfate

Calcium carbonate

Magnesium bromide

Sodium nitrate



Composition of compounds

A compound contains atoms from different elements that are chemically joined together.

A compound always contains a particular amount of each element. It has a fixed composition.

Compound names can get quite long and complicated, so the symbols of the elements are used as a shorthand.

The symbols of the elements in a compound are combined to give the formula of the compound.

What is the formula of carbon dioxide ?


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A formula uses the symbols of the elements in a compound.

When there is more than one atom of each element, the number is always written after the symbol .

carbon dioxide carbon atom = 1 oxygen atoms = 2 formula =

CO

2 water hydrogen atoms = 2 oxygen atom = 1 formula =

H

2

O

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The formula shows the ratio of atoms in a compound.



What is the formula of each of these compounds?

(In a formula put the metal first as when naming a compound.)

1.

Titanium oxide

For every titanium atom there are two oxygen atoms.

Formula = TiO

2

2.

Lithium oxide

For every two lithium atoms there is one oxygen atom.

Formula = Li

2

O

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3.

Aluminium chloride

For every aluminium atom there are three chlorine atoms.

Formula = AlCl

3



What is the formula of each of these compounds?

(In a formula put the metal first as when naming a compound.)

1.

Silicon chloride

For every silicon atom there are four chlorine atoms.

Formula = SiCl

4

2.

Manganese oxide

For every manganese atom there are two oxygen atoms.

Formula = MnO

2

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3.

Aluminium oxide

For every two aluminium atoms there are three oxygen atoms.

Formula = Al

2

O

3



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•Work safely in the lab to make compounds from elements


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Chemical reactions

The substances that react are called the

REACTANTS.

The substances formed are called the

PRODUCTS.

REACTANTS PRODUCTS

To represent chemical reactions we write

word equations

or

symbol equations

.


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A word equation can be used to describe any chemical reaction, i.e. any process in which atoms become joined in different ways.

The steps for writing a word equation are:

1.

On the right-handside, put the name of the reactant ( s ).

If there are two or more reactants, link them with a + sign.

2.

In the middle, write down an arrow (  ).

3.

On the right-handside, put the name of the product ( s ).

If there are two or more products, link them with a + sign.



Lead reacts with oxygen to form lead oxide.

What is the word equation for this reaction?

lead + oxygen  lead oxide

Why is lead oxide so different to both lead and oxygen?

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The lead and oxygen don’t mix, they react to form lead oxide.

This means that the lead and oxygen atoms in the product are joined differently to the atoms in the reactants .



Chemical reactions, continued

Write word equations for the following reactions

1 When sodium is burned in oxygen, sodium oxide is formed.

sodium(s) + oxygen(g) sodium oxide(s)

2 When solid calcium carbonate is heated, it decomposes into solid calcium oxide and carbon dioxide gas.

Calcium carbonate(s) heat calcium oxide(s)

+ carbon dioxide(g)


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Write out word equations for the following chemical reactions.

1.

Limestone (calcium carbonate) is heated to make calcium oxide and carbon dioxide.

calcium carbonate  calcium oxide +carbon dioxide

2.

Magnesium reacts with hydrochloric acid to make magnesium chloride and hydrogen.

magnesium + hydrochloric acid  magnesium chloride + hydrogen

3.

Methane is burnt to make carbon dioxide and water.

methane + oxygen  carbon dioxide + water

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Investigation: For each of the following;

1. Complete the experiment & write an observation

Write a word equation

Write a symbol equation

Balance the equation

Describe the ratio of atoms in the compound composition of the products

• Burn magnesium

• Pour hydrochloric acid over magnesium

• Pour sulphuric acid over zinc


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1) When calcium carbonate burns it turns …..(complete the experiment & write an observation)

2) calcium carbonate  calcium oxide +carbon dioxide complete the word equation

3) CaCO

3(s)

CaO

(s)

+ CO

2(g) complete the symbol equation

4) 1 Ca

1 C

3 O

1 Ca

1 C

3 O balance the equation

5) 1 Calcium atom to every 1 oxygen atom AND 1 carbon atom to every 2 oxygen atoms. describe the ratio of atoms in the compound composition of the products

6) complete diagrams of at least one of the equations

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Does the mass change during a chemical reaction?

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For example, when 56 g of iron reacts with 32 g of sulfur iron sulfide is formed. The mass of the iron

When 48 g of magnesium is heated in oxygen, 80 g of magnesium oxide is formed. What mass of oxygen is needed to react with the magnesium?



Burning fossil fuels

The three fossil fuels are:

Coal, oil and natural gas.

When the fossil fuels are burned in enough air they always form water and carbon dioxide. Carbon

Write the word equation for methane (natural gas) burning in oxygen.

methane(g) + oxygen(g) carbon dioxide(g) + water(l)


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The Reactivity Series

Metals are arranged in order of how reactive they are. A more reactive metal will displace a less reactive one from its compounds.

For example, zinc will displace copper from copper sulfate to give zinc sulfate plus copper.

The word equation is: zinc(s) + copper sulfate(aq) zinc sulfate(aq) + copper







•Work safely in the lab to make compounds from elements


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8F Compounds and Mixtures - science

Mixtures –

The substances formed are called the

To represent chemical reactions we write

or

.

Write a word equation

Balance the equation

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8F Compounds and Mixtures - science

Mixtures –

The substances formed are called the

To represent chemical reactions we write

or

.

Write a word equation

Balance the equation

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