Y7 - Science - Chemistry

Matter

The material from which things are made up from. Takes up space. Can exist as a solid, liquid, or gas

Solid

Have a fixed volume and cannot be compressed.

Liquid

Has a fixed volume, but doesn’t have a fixed shape

Gas

No fixed volume or shape.

Particle Model

• All matter is made up of tiny particles. 

• The particles of matter are always moving. 

• The particles have spaces between them. 

• Adding heat to matter makes the particles move faster. 

Evaporation

Liquid turns into a gas. Increase in temperature.

Condensation

Gas turns into liquid. Decrease in temperature.

Melting

Solid turns into liquid. Increase in temperature.

Freezing

Liquid turns into solid. Decrease in temperature.

Density

The measurement of quantity or mass per unit of volume in a particular substance.

Mass ➗ Volume

Melting Point

The temperature at which a given solid will melt

Compressibility

The capacity of something to be flattened or reduced in size by pressure.

Boiling point

The temperature at which a liquid changes into a gas

Pure substance

Made from only one chemical element or one compound.

Sublimation

When a solid turns into a gas

Deposition

When a gas turns into a solid

Atom

The basic building blocks of matter that retains its properties

Element

Any substance that cannot be decomposed into simpler substances by ordinary chemical processes. The fundamental materials of which all matter is composed.

Compound

A material formed by chemically bonding two or more different chemical elements

Impure Substance

A substance made from more than one element or one compound

Pure substance

Made up of only one type of particle (atom, molecule, or compound)

Proton

A subatomic particle. Has a positive electric charge. Found in the nucleus.

Neutron

A subatomic particle. A neutral (no charge) electric charge. Found in the nucleus of all atoms except Hydrogen.

Nucleus (of an atom)

Consisting of protons and neutrons at the center of an atom.

The nucleus is positively charged, due to the fact that there are no electrons in it.

Electron

Subatomic particle. Negative electric charge. Found orbiting the nucleus in shells. Add very little mass to the atom.

The Periodic Table

A display of elements ordered according to their atomic number. It orders elements into rows and columns based on their properties. 

Groups

Vertical columns numbered 1-18 of the periodic table. Helps to determine the number of valence electrons of an element’s atom.

Periods

The horizontal rows of elements. Represent the number of electron shells an atom has.

Metals

Found on the left-hand side of the Periodic table and account for the majority of the known elements.

Having a luster (shiny). 

Being malleable in their solid state. In other words they can be bent into shape. Gold is the most malleable of all the metals

Ductile – can be drawn into a wire. Silver is one of the most ductile metals

Able to conduct heat and electricity

Most metal’s have high boiling points

Usually more dense than non-metals

(Most are) Silvery in colour, although some like gold, cesium and copper are coloured.

Non-Metals

Found on the far right side of the Periodic table. Most are either gases or solid, with the exception of bromine, which is a liquid.

They are:

Dull (not shiny)

Brittle (therefore can’t bend and will break instead)

Poor conductors of heat and electricity

Lower melting and boiling points than metals

Metalloids

Small group of elements that are found in between the metals and non-metals.

Dull or lustrous

Semiconductors of electricity

Brittle

They are Silicon and Boron.

Atomic Number

Represents the number of protons that element has in its nucleus.

Atomic mass

The average mass of the atom’s element measured in atomic mass unit (amu).

Protons + Neutrons

Mixture

Otherwise known as an impure substance, it contains two or more substances that are not chemically combined.

Sediment

Formed at the bottom of a liquid from the process in which insoluble particles separate from that liquid because of gravity.

Solution

Homogeneous mixture of one or more solutes dissolved in a solvent.

Solute

The substance that dissolves in a solvent to produce a homogeneous mixture.

E.g. The salt being placed in water to make salt water

Solvent

Any substance, usually liquid, capable of dissolving one or several substances, thus creating a solution.

Solubility

Defined as the maximum amount of a substance that will dissolve in a given amount of solvent at a specified temperature.

Soluble

When it is capable of being dissolved in some solvent (usually water)

Insoluble Substance

A substance (solid) that will not dissolve in a solvent even after mixing

Concentration

The amount of a substance in a given amount of another substance

Dilute (solution)

Which there is a relatively small amount of solute dissolved in the solution

Supersaturated solution

A solution that contains more than the maximum amount of solute that is capable of being dissolved at a given temperature.

Filtration

Can be used to separate insoluble solids from a liquid. It uses a filter. The holes in a filter are usually too small to see, but solid pieces get trapped whereas the liquid and anything soluble pass through.

Separates based on differences in particle size and solubility.

Decanting

A simple separation technique used to separate a liquid (and anything dissolved in it) from an insoluble solid – meaning a solid that doesn't dissolve.

Useful for separating suspension mixtures.

Gravity causes the solid particles to settle at the bottom, forming sediment. Solid at bottom, liquid at top.

Relies on difference in density.

Magnetism / Magnetic Separation

Used to separate mixtures where one part is magnetic and the other is not. Uses a magnet to attract magnetic materials, while the non-magnetic parts stay behind.

Doesn’t require any heating or chemicals, just a magnet.

E.g. Recycling: Removing steel cans from a pile of mixed waste. Mining: Separating magnetic iron ore from rock.

Distillation

A separation technique used to separate mixtures based on differences in boiling points. It involves heating a liquid to create vapour, which is then condensed back into liquid to collect the distillate.

Centrifuging

A method used to separate mixtures with different densities by spinning them very quickly around a fixed point. This process creates a strong centrifugal force that pushes denser materials outward, separating them from lighter substances.

e.g. Washing machines.

Evaporation

The process where liquid turns into a vapour.

Separate soluble solids from the solvent they have dissolved in.

Relies on boiling point.

Crystallisation

A solution heated very gently. As the solution is heated, some of the solvent evaporates. The remaining solution becomes more concentrated. Once hot, this concentrated solution is then removed from the heat and allowed to cool. As the solution cools, solid crystals will form.

Separate soluble solids from the solvent they have dissolved in.

Relies on solubility and boiling point.

Hand Picking

The separation by hand of desired particles from a mixture containing undesired particles. 

Winnowing

A separation method that is designed to remove lighter particles while maintaining heavier ones. It is commonly used in separating seeds from their outer shells or coatings (husks).

Yandying

Similar to winnowing. The yandy is held in the hand, raised in one corner, and then gently shaken back and forth forcing the smaller and denser particles to collect at the bottom while the larger and less dense particles remain higher up.  

Sieving/Filtering

Pushing a mixture through a physical barrier with small holes or gaps to separate the larger particles from the smaller ones.

Cold-pressing

A separation technique that uses pressure to extract oils from plant matter. No heat is used in the process.

Distillation

A process that separates a mixture of liquids based on their differences in boiling points.

Residue

The solid or insoluble component left in the filter after the process of filtration. 

Separation Techniques at Home

• Using sieves to separate pasta from water 

• Decanting oil from vinegar in salad dressings 

• Filtering tea leaves from brewed tea 

• Evaporating water from clothes that dry in the sun

Desalination plants

Turn seawater into fresh water by using thermal desalination, or membrane desalination. In thermal desalination, they use distillation – evaporate the water, then condense the water vapor. There are two types of membrane desalination: reverse osmosis, and electro-dialysis.

Possible environmental impacts can on marine life is that tiny micro-organisms, such as planktons, can get sucked into the machine too.

Reverse osmosis

Seawater is pushed through, with high pressure, a special filter paper, that can catch salt and other small things. In electro-dialysis, salt from the seawater is removed with electricity.