atoms, elements and compounds

what is the difference between a chemical and physical change?

• physical is when the substance changes its physical state

• eg: ice to water

• chemical is when a new substance is formed during a chemical reaction

describe elements

• any substance that can’t be broken down into a simpler one

• only made up of one type of atom

what are the properties of metals?

• usually solid at room temp

• malleable and ductile

• usually high melting and boiling points

• good conductivity of heat and electricity

what are the properties of non metals?

• solid, liquid or gas at room temp

• usually soft or brittle

• usually low melting and boiling point

• very poor conductivity of heat and electricity

describe compounds

• they’re pure substances which have two or more elements

• eg; H2o or water

what is the difference between mixtures and compounds?

• substances in a mixture have not had a chemical reaction

• may be easy to separate them physically

• compounds have had a chemical reaction

• the properties are very different to the components

what is an exothermic reaction?

when heat energy is given out during a reaction

what is found in atoms?

• protons (+ charge) and neutrons (no charge) which are in the nucleus

• electrons (- charge) surround the nucleus

what is the atomic number equal to?

the number of protons in an atom

what is the nucleon number?

the total number of protons and neutrons

describe isotopes

they’re atoms of the same element which have a different number of neutrons but the same number of protons

what is electronic configuration?

• 2,8,8

• the outer electrons are mainly responsible for an elements chemical properties

• so elements in the same groups have similar ones

why do outer shell electrons become easier to lose?

• because they get farther away from the nucleus

• so there is less attraction between the nucleus and the outer shell electrons

• because of the increased distance

what are ions?

• electrically charged particles

• an atom becomes an ion when is loses or gains electrons

describe ionic bonding

• compounds with metal and non metals

• electrons are transferred from metal to non metal atoms when this bond is formed

• the atoms become more stable by getting full outer energy levels

what are the properties of ionic structures?

• usually solids at room temp

• have high melting and boiling points due to the strong electrostatic forces

• ions are packed together in a lattice (regular arrangement)

• cannot conduct electricity when solid because ions aren’t free to move

• only in molten state

describe covalent bonding

• compounds with non metals

• shares electrons

what are the properties of covalent compounds?

• simple molecular substances, usually gases liquids or solids

• low melting and boiling point bc of the weak intermolecular forces of attraction

• generally don’t conduct electricity when molten bc they don’t have ions

what is an allotrope?

when an element can exist in more than one physical form

what are the allotropes of carbon?

graphite, diamond

what are the properties of graphite?

• has 3 covalent bonds

• has a delocalised electron which allow graphite to conduct electricity

• shiny

• conducts electricity

• soft material

• uses: pencil, lube

what are the properties of diamond?

• no delocalised electrons to enable diamond to conduct electricity

• colourless

• doesn’t conduct electricity

• very hard

• uses: jewellery, polishers

what are the use of metals?

• electrical cables bc it has good electrical conductivity

• making cars, bikes etc