CHEMISTRY EDEXCEL IGCSE DOUBLE SCIENCE

Element

substance that consists entirely of one type of atom, cannot be broken down into anything simpler by known chemical means

Ion

A charged particle formed when an atom either loses electrons to become positively charged, or gains electrons to become negatively charged

Group

Vertical column in the periodic table, determines the number of occupied energy levels in an element

noble gases

monoatomic gases in group 8/0

period

horizontal row in the periodic table

Halogens

non-metals in group 7

alkali metals

metals in group 1

alkaline earth metals

metals in group 2

transition metals

metals in the central block of the periodic table

how the modern periodic table is organized

by increasing atomic number

the side most non-metals are found on the periodic table

right

the side metals are found on the periodic table

left

properties of metals

high melting points, good thermal conductors, high density, malleable, ductile

state of most metals at room temperature

solid

metal oxide + water

(alkaline) metal hydroxide

properties of non-metals

poor conductors of electricity, good thermal conductors, good insulators, brittle, low melting points

more reactive metal + salt solution →

salt solution + metal

more reactive metal + less reactive metal oxide →

metal oxide + metal

Where electrons are found

energy levels

minimum number of electrons in a full outer shell

2

electron configuration

the arrangement of electrons in an atom

why noble gases are unreactive

They have a full outer shell of electrons, so they do not need to gain/lose electrons

how ions are formed

atoms gain/lose electrons to obtain a full outer shell

what is formed when metals lose electrons?

positively charged ions/cations

what is formed when metals gain electrons?

negatively charged ions/anions

what is the charge on ions formed from a group 1 metal?

1+ ions

what is the charge on ions formed from a group 2 metal?

2+ ions

what is the charge on ions formed from a group 3 metal?

3+ ions

what is the charge on ions formed from a group 5 non-metal?

3- ions

what is the charge on ions formed from a group 6 non-metal?

2- ions

what is the charge on ions formed from a group 7 non-metal?

1- ions

ionic bond

strong electrostatic force of attraction between oppositely charged ions

why there are high melting and boiling points in giant ionic structures

strong electrostatic forces of attraction between the oppositely charged ions holding the giant ionic lattice together need a large amount of energy supplied in order to break the many strong electrostatic forces of attraction

giant ionic structures

compounds with ionic bonding

why giant ionic structures are crystalline solids at room temperature

due to the regular, alternating arrangement of the billions of oppositely charged ions in the giant ionic lattice

why giant ionic compounds are poor conductors of electricity in solid form

the ions are held in fixed positions in the giant ionic lattice and are unable to move freely

why giant ionic compounds are good conductors of electricity in molten form or in solution

the ions are now free to move around in solution

why giant ionic compounds tend to be soluble in water

the ionic compound dissolves in water, the giant ionic lattice is split up by attractions with the water molecules, so the ions are free to move around in solution

why giant ionic compounds tend to be brittle

any small distortion in the giant ionic lattice will bring ions with the same charges next to each other - like charges repel and hence the crystal is split apart

Atom

the smallest particle of an element that is still recognisable as that element

Molecule

A substance made up of two or more atoms bonded together

atomic number

the number of protons in the nucleus of an atom, defines the element

atomic mass number

number of protons and neutrons in the nucleus of an atom

Isotopes

Atoms with the same atomic number (same number of protons) but different numbers of neutrons (different mass number)

relative atomic mass

The weighted average mass of an atom of an element, taking into account its naturally occuring isotopes, relative to 1/12th of the mass of an atom of carbon-12

what atoms consist of

protons, neutrons, electrons

number of neutrons

mass number - atomic number

number of electrons/protons

atomic number

relative atomic mass equation

Ar (element) = (Ar (isotope 1) x %abundance) + (Ar (isotope 2) x % abundance)

alkali metals names

Lithium, Sodium, Potassium, Rubidium, Caesium, Francium

Lithium electron configuration

2,1

Sodium electron configuration

2,8,1

Potassium electron configuration

2,8,8,1

Alkali metals physical properties

good conductors of heat and electricity, soft and can be cut, low density for a metal - they float, low melting point for a metal

Alkali Metals Chemical Properties

All have one electron in their outermost shell, giving them similar properties, have to lose one electron to achieve a full outer shell, very reactive, react violently with water, in water they form hydrogen gas and metal hydroxide

lithium appearance

soft, silvery-white solid

Sodium appearance

soft, silvery-grey solid

potassium appearance

very soft, silvery-grey solid

observation of alkali metals reacting with oxygen

when freshly cut their surface turns from dull to shiny

the reaction is faster as you go down the group

what is produced with alkali metals react with oxygen

metal oxide

observations from the reaction of lithium with water

effervescence, floats and moves on the water's surface leaving a trail, metal disappears, heat and hydrogen gas is given off

observations from the reaction of sodium with water

rapid effervescence, floats and moves quickly on the surface of the water, melts to form a sphere due to increased heat from the reaction, metal disappears faster, heat and hydrogen gas is given off

observations from the reaction of potassium with water

vigorous effervescence, floats and moves very rapidly across surface of water, very exothermic, gas evolved ignites instantly, metal also set on fire to give lilac flame, metal disappears very quickly, 'spits' at the end of the reaction, heat and hydrogen gas given off

order of relative rate of reaction

Li<Na<K

colour universal indicator turns after water and alkali metals have reacted

purple

why reactivity increases as you go down group 1

outermost electron gets further from the nucleus as shielding energy levels increase, hence the attraction between the negative valence electron and positive nucleus becomes weaker as you go down the group - valence electron is held less tightly in K than Li, so is more easily lost

physical properties of halogens

form coloured vapours, melting and boiling points increase hence state changes from gas to liquid to solid as you go down the group, halogens become less toxic and corrosive and colour of halogens get darker as you go down the group

chemical properties of halogens

seven electrons in their outermost energy level, gives them similar chemical properties, need to gain one electron to become a negatively charged ion, known as a halide

fluorine appearance at room temperature/vapour colour

yellow gas

chlorine appearance at room temperature/vapour colour

green gas

bromine appearance at room temperature

Red-brown liquid

Bromine vapour colour

orange-brown

iodine appearance at room temperature

dark grey solid

Iodine vapour colour

purple

hydrogen fluoride balanced symbol equation

H₂ (g) + F₂ (g) -> 2HF (g)

hydrogen chloride balanced symbol equation

H₂ (g) + Cl₂ (g) -> 2HCl (g)

hydrogen bromide balanced symbol equation

H₂ (g) + Br₂ (g) -> 2HBr (g)

hydrogen iodide balanced symbol equation

H₂ (g) + I₂ (g) -> 2HI (g)

Chlorine reaction with iron wool

iron wool burns and glows brightly when chlorine passed over it, vigorous reaction without heating needed, clouds of brown 'smoke' seen

Bromine reaction with iron wool

hot iron wool glows but less brightly, less vigorous reaction, yellow-brown solid formed on iron wool

Iodine reaction with iron wool

hot iron wool gives a dull glow, slow reaction, red-brown solid formed on iron wool

what is formed when halogens react with iron

iron (III) halide

why reactivity decreases as you go down group 7

halogens must gain one electron to form a negatively charged ion - outermost electron gets further from the nucleus as shielding energy levels increase, hence the attraction between the negative valence electron and positive nucleus becomes weaker as you go down the group, so much less attraction in I than in F, so harder to attract and hold the extra electron in I rather than F, so fluorine is most reactive and iodine is least reactive

displacement reaction

the more reactive halogen will displace the less reactive halogen from its compound

chlorine water and sodium bromide reaction observation

colourless solution turns yellow-orange

chlorine water and sodium iodide reaction observation

colourless solution turns brown

bromine water and sodium chloride reaction observation

solution remained yellow-orange

bromine water and sodium iodide reaction observation

solution darkens to brown

iodine water and sodium chloride reaction observation

solution remained brown

iodine water and sodium bromide reaction observation

solution remained brown

what the colour of the resulting solution tells you in a displacement reaction

if there is a halogen present - if you did not start with this halogen a displacement reaction has taken place

chlorine + sodium bromide balanced symbol equation

Cl₂ (aq) + 2NaBr (aq) -> 2NaCl (aq) + Br₂ (aq)

chlorine + sodium iodide balanced symbol equation

Cl₂ (aq) + 2NaI (aq) -> 2NaCl (aq) + I₂ (aq)

bromine + sodium iodide balanced symbol equation

Br₂ (aq) + 2NaI (aq) -> 2NaBr (aq) + I₂ (aq)

OIL RIG

Oxidation Is Loss, Reduction Is Gain of electrons

redox reaction

reduction and oxidation occuring in the same reaction

oxidising agent

accepts electrons, is reduced

oxidising agent example

chlorine

reducing agent example

bromide ions