Elements, Compounds, Mixtures & Chemical / Physical Change

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CHAPTER 6

Every substance is made up of atoms

Elements

Metallic Elements

Tend to be shiny

Solid at room temperature

Good conductors of heat and electricity

Can be bent and hammered into sheets

Can be stretched into wires

Non - Metallic Elements

Tend to be solids of gases at room temperature

Usually are dull

Don’t conduct heat or electricity

Break or cruel when you bend them

118 elements in the Periodic Table

Chemical symbols of an element is usually 1 or 2 letters, mostly corresponding with the elements full name e.g. h for hydrogen

Atoms in Elements

Elements are made up of just 1 type of atom however they can be found as:

single atoms - monatomicrare

in clusters - moleculestwo or more atoms bonded (joined) together, molecules are identical; same shape, size and type of atom

large grid like structures - latticescrystal lattices are large grid like structures hat repeat the same arrangement of atoms over and over. All metallic elements form crystal lattices as well as very few non - metallic elements

Compounds and MixturesMost substances you encounter every day are made up of more than one type of atom. These are called compounds.

Compounds

Molecular Compoundsall molecules in a compound are identical in shape, size and number of atoms

Compound Latticescompounds can also form crystal lattices. In these lattices, the atoms are bonded very strongly to each other so they tend to be very hard solids at room temperature

Mixtures

Mixes of elements and compounds are referred to as ‘mixtures'

You cannot write chemical formulas for mixtures

Solution

when a solid dissolves in a liquid

dissolving solid is known as the ‘solute'

the liquid which the solid dissolves in is known as the ‘solvent'

if the solid is insoluble, the mixture can be named a ‘colloid’ or ‘suspension'

colloid - solute is not have enough to sink to the bottom

suspension - solute sinks to the bottom

solutions where liquids dissolve in other liquids are known as miscible

solutions where liquids can’t dissolve one another are known as immiscible

Alloysa mixture of metal with other metals or non-metals

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CHAPTER 7

Physical Change

The key feature of physical change is that no new substance is produced during the change

Can be easily reversed

Properties

change in shapeforce is applied to

bend the object

break the object

crumble the object

stretch the object

twist the object

compress the objecteg. you can bend aluminium and there will be a change in shape but it is still only physical change because in the end it is still aluminium.

formsame concept was shape

expansion / contraction

when the temperate of the substances changes

melt: change to a liquid - when heated enough

freeze: becomes a solid - when cooled enough

evaporate - when a liquid is warmed and becomes a gas

condensation - when a gas cools and becomes a liquid

in solids, the particles vibrate in fixed positions. as the temperature increases, so do the vibrations - pushing the particles further apart slightly and causing the object to expand. when the solid is cooled, the vibration rate lowers and it allows the particles to be packed closer together, causing contraction.

the particles in liquids also vibrate more when they are heated. this causes liquids to expand when heated and contract when cooled. However, in liquids the particles are free to move, so liquids tend to expand and contract more than solids.

gases will always expand or contract to fill their container. however, as the temperature of a gas is increased, the particles travel faster. this means they hither sides of their container more frequently and with more force.

change in state

liquid

gas

solid

mixing substances togethereg. plastic balls of different colours - when mixed no new colour ball is formed.

Most physical changes can be understood by using the particle model. It can explain the basis of their properties

Solids are incompressible and hold their shape.In solids, the attraction between particles binds them tightly together. For this reason, solids are incompressible and hold their own shape. Although the particles in solids are in a fixed position, they vibrate on the spot. here vibrations increase with temperature

Liquids are incompressible and flow to take the shape of the bottom of their containerIn liquids, the particles are packed tightly together, which makes liquids incompressible. However, the particles in a liquid are not stuck together as much as they are in solids. his gives liquids the ability to low and on the shape of the bottom of heir container. Particles in a liquid vibrate but an also move freely through the liquid.

Gases are compressible and fill their containerIn gases, the particles are not stuck to each other at all and there are large spaces between them. or this reason, gases are highly compressible. The particles are free to move anywhere within their container. The particles move in straight lines until they collide with another gas particle or the side of the container.

Chemical Change

A new substance HAS been formed

Hard / Impossible to reverse

The atoms in the original substance have been rearranged

In a chemical reaction, the old substances are known as the reactants and the new products are called the products

Properties

a permanent change in colour

smelling gas or seeing bubbles

fizzy

different smell

smoke

seeing a new solid (known as a precipitate) forming in a clear solutionthe solid ‘falls’ out of the solution and sinks to the bottom

change in temperature