© Boardworks Ltd 2003 Solid Natural Metal Element Millions of substances There are millions of substances and as a first step to understanding them scientists.

© Boardworks Ltd 2003

Solid

Natural

Metal

Element

Millions of substances

There are millions of substances and as a first step to understanding them scientists sort these substances into various types or groups.Here are some of the more common ways of grouping substances.There are far fewer elements than substances.

Liquid Gas

Synthetic

Non-metal

Compound Mixture

In this unit the focus is mainly

upon atoms and elements.


Elements

• Elements are the building blocks for all other substances.

• A small number of types of brick can be used to create an enormous range of different buildings.

• In much the same way a small number of elements can give rise to an enormous number of compounds.

A small number of different types of

Lego Brick can be used to create a huge number of different models!


Elements and Atoms

• All substances are made of atoms but only about a hundred substances contain just one type of atomjust one type of atom.

• These are the simplest (or most elementary) substances in the universe.

• They cannot be broken into anything simpler : you cannot get simpler than having just one type of atom! These are elementselements.

Fe

FeFe

Fe

Elementary dear Watson!


A molecule of the element

hydrogen

H H

Elements and Compounds

Compounds are produced when elements combine together during a chemical reaction

It follows that compounds contain two or more types of two or more types of atom.atom.

A molecule of the

compound water

H H

O

Mg + acid

hydrogenLighted splint

Oxygen in the air

Oxygen in the air

Elements are materials made up of one type of atom onlyone type of atom only


Compounds: Water

Compounds are produced when elements combine.E.g. 1. Water

Hydrogen

Oxygen+

Reaction

Water

Word Equation

Hydrogen + Oxygen Water

H

H H

HO O H

OH

HO

H


Compounds – not mixtures

• The atoms in compounds are NOT mixed together

• They become bondedbonded together during a chemical chemical reaction.reaction.

• Because of this:

• Compounds have properties that are veryvery different to the elements that they are made from.

HYDROGEN

Flammable gas

OXYGEN

Gas in which many

substances burn

WATER

Liquid that extinguishes

most fires+


E.g. Carbon dioxide

Compounds: carbon dioxide

carbon dioxide+

carbonoxygen

Reaction


Compounds – not mixtures

CARBON

Black solid used as

barbecue fuel

OXYGEN

Gas in which many

substances burn

+

CARBON DIOXIDE

Gas used in fizzy drinks and fire extinguishers

O OC C OOReaction

Word equation

carbon + oxygen carbon dioxide


Activity


Chemical Reactions: changes in bonding

During chemical reactions atoms become bonded (joined) together in new ways.

Magnesium + Copper Oxide Magnesium Oxide + Copper

Mg Cu O Mg O Cu

Chemical reactions are different to physical changes.

In physical changes atoms remain bonded in the same way before and after a change.

Water ice

OHH

OH

H

OH

H

OH

H

OH

H

OH

H


Reactants and Products

In chemical reactions new substances are formed. We call the starting materials reactantsreactants and the substances that are formed: productsproducts. For example -

Substance Reactant or Product?magnesium oxide

magnesium

copper oxide

copper

product

reactant

reactant

product

Mg Cu O Mg O Cu+ +


Word Equations

Chemists often use word equations as a way of quickly telling us what the reactants and products are.

We just write:– the names of the reactants–an arrow (meaning reacts to give)–the names of the products

For example, for magnesium reacting with copper oxide to form magnesium oxide and copper we write -

Magnesium + Copper Oxide Magnesium Oxide + Copper


1. Magnesium burned brightly reacting with the oxygen in the air to form magnesium oxide.

magnesium + oxygen magnesium oxide

2. Hydrochloric acid reacted with the calcium hydroxide to give water and calcium chloride

hydrochloric acid

+ calcium hydroxide

water + calcium chloride

3. Electrolysis of aluminium oxide produced aluminium metal and oxygen gas

aluminium oxide aluminium + oxygen

Write word equations for these reactions:


No new atoms

Note that chemical reactions can produce very different looking substances.

This is because atoms have bonded (joined) together in new ways.

It is notnot because any new atoms have been formed.

Mg Cu O Mg O Cu

1 Mg 1 Cu 1 O

The same number of each type of atom are present before and after a chemical reaction.

+ +


In a chemical reaction all the atoms present in the reactants are also present in the products.

It follows that the mass of the reactants will be equal to the mass of the products.

Mg Cu O Mg O Cu

Total mass of reactants = total mass of products

This is known as the Law of Conservation of MassLaw of Conservation of Mass

Total Mass = mass of:

1Mg, 1 Cu and 1 O atom

Total Mass = mass of:

1Mg, 1 Cu and 1 O atom

+ +

No change in total mass


The Conservation of Mass Conservation of Mass only works if you include the mass of all the reactant and product atoms.In reactions that produce a gas mass may appearappear to be lost. This is because some of the atoms have left the flask in which we are carrying out the reaction. E.g. When magnesium reacts with acid if we also weigh the hydrogen that has been given off then we find mass isis conserved.

MgH Cl

H Cl H

HMg

Cl

Cl+

+

Hydrogen leaves the flask and so products appearappear to have less mass




We can demonstrate the Law of conservation of mass using any reaction where no gas is “lost.”

We can look at the reaction:

Colourless solution

Yellow solid

Colourless solution

Colourless solution

Lead nitrate + potassium iodide lead iodide + potassium nitrate


Elements and Symbols

• Chemists have agreed symbols that they use to represent elements. This means that they can use just a couple of letters rather than the full name and chemists everywhere in the world know which element they mean.

• Many of the more common elements just use the first letter of the name

O OxygenN NitrogenC CarbonF Fluorine

• Others use two letters

• …And they’re not always what you might expect

Ca CalciumClAlMg ChlorineAluminium

Magnesium

Fe IronNa SodiumCu CopperPb Lead


Writing Symbols

There are some important rules about how to write symbols. Ignoring these can lead to confusion about what they mean

1. If the symbol has just one letter make it a capital letter

E.g. Nitrogen is N N not nn

2. If the symbol has two letters make the first a capital letter and the second a small letter

E.g. Cobalt is Co Co not COCO CO

No Watson, carbon

monoxide poisoning – not cobalt


Elements and the Periodic Table

• The Periodic Table uses the symbols of elements.

• It arranges these symbols in a way that helps chemists remember what elements are like.


The Periodic Table


H

Li

Na

K

Rb

Cs

Fr

Be

Sc Ti

Mg

V Cr Mn Fe Co Ni Cu Zn Ga Ge Se BrCa Kr

Y Zr Nb Mo Tc Ru Pd Ag Cd In Sn SbSr TeRh

Ba Hf Ta W Re Os Ir Au Hg Tl Pb Bi PoLa AtPt

Ra Rf Db Sg Bh Hs Mt ? ?Ac ?

Al P

N O

S Cl

F Ne

Ar

Rn

I

Si

Xe

He

B C

AsFeFe

Metals and Non-metals

Do you think these are metals or non-metals?

Mg SPMg SP

CuCu

metal Non-metal

IISb

Hard to say!

Sb

Activity



• Metals are on the left and centre.

• Non-metals are mostly on the right

• In between are metalloids – these are like metals in some ways and like non-metals in others.

Metals and non-metals have very different physical properties. Because of this the position of metals and non-metals show a pattern in the Periodic Table:


Non-metals and Metals



Say whether these elements are metals, non-metals or metalloids

H

Li

Na

K

Rb

Cs

Fr

Be

Sc Ti

Mg

V Cr Mn Fe Co Ni Cu Zn Ga Ge Se BrCa Kr

Y Zr Nb Mo Tc Ru Pd Ag Cd In Sn SbSr TeRh

Ba Hf Ta W Re Os Ir Au Hg Tl Pb Bi PoLa AtPt

Ra Rf Db Sg Bh Hs Mt ? ?Ac ?

Al P

N O

S Cl

F Ne

Ar

Rn

I

Si

Xe

He

B C

As

Silicon (Si) MetalloidFrancium (Fr) MetalScandium (Sc) MetalKrypton (Kr) Non-metalCobalt (Co) Metal

Activity



Metals vs Non-metals




Elements and Molecules

• An element is a substance which contains only one type of atom.

HoweverHowever

• This does not mean that some atoms do not join together.

• For example, in hydrogen gas the atoms always exists in groups of two. Phosphorus atoms exist in groups of four and so on.

Molecules of an element.

H H HH

HH

Atoms of an element

A molecule is a group of atoms that are joined (bonded) together.


Elements and Molecules 2

Only non-metalsnon-metals join into small groups to form molecules. You should know that the following elements exist as molecules with twotwo atoms.

O2OOxygen

N2NNitrogen

I2IIodine

Br2BrBromine

Cl2ClChlorine

F2FFluorine

H2HHydrogen

FormulaSymbolElement

H H

F F

Cl Cl

Br Br

I I

O O

N N


1. Which of these elements is a liquid?

A. bromine

B. iodine

C. oxygen

D. aluminium


2. Which of these is NOTNOT a typical property of metals?

A. conduct

B. strong

C. dense

D. brittle


3. What is the symbol for Gold?

A. Go

B. Au

C. Ag

D. au


4. Which of the following elements is not a metal?

A. copper

B. lead

C. lithium

D. neon


5. Which of the following elements exists as a molecule?

A. bromine

B. mercury

C. beryllium

D. tin

© Boardworks Ltd 2003 Solid Natural Metal Element Millions of substances There are millions of substances and as a first step to understanding them scientists.

Documents

element hydrogen h h

elements elements

compounds compounds

water compounds

carbon dioxide compounds

elementary substances

small number of elements

fewer elements