chem y10 mid years

what side are reactants in a chemical reaction

left hand side

what side are products in a chemical reaction

right hand side

what does the state symbol ‘(s)’ mean

solid

what does the state symbol ‘(l)’ mean

liquid

what does the state symbol ‘(g)’ mean

gas

what does the state symbol ‘(aq)’ mean

aqueous

formula of water

H2O

formula of ammonia

NH3

formula of carbon dioxide

CO2

formula of chlorine

Cl2

formula of ammonium (ion)

NH4+

formula of hydroxide (ion)

OH-

formula of nitrate (ion)

NO3-

formula of carbonate (ion)

CO3 2-

formula of sulfate (ion)

SO4 2-

hazard meaning

something that could potentially cause harm

risk meaning

the chance that a hazard will cause harm

the plum pudding model

An early model which was based on a scientific idea on atomic structure was the plum pudding model. In this model, it was believed the atom was a sphere of positive charge with negatively charged electrons scattered around the atom like plums in a pudding

relative charge of protons

+1

relative charge of neutrons

0

relative charge of electrons

-1

relative mass of protons

1

relative mass of neutrons

1

relative mass of electrons

0.0005

radius of atom

1 × 10^-10m

what does the atomic number tell you

the number of protons in an atom

what does the mass number of an atom tell you

the total number of protons and neutrons in the nucleus

what is an isotope

atoms with the same number of protons but a different number of neutrons

why are some rfms of elements not whole numbers

the rfm is the average mass of all the isotopes of the element, so sometimes they aren’t whole numbers

how did mendeleev organise the periodic table

in order of increasing atomic mass

how is the modern period table organised

in order of atomic number

vertical columns in the periodic table are called..

groups

horizontal rows in the periodic table are called..

periods

as you go down a group in the periodic table, the ___ increases

number of valence shells

electronic configurations arranged..

2, 8, 8, etc

what is an ion

an atom with a positive or negative charge due to losing or gaining electrons

negative ion

anions

positive ions

cation

ions ending with -ate are..

negative ions containing oxygen and at least one other element

ions ending with -ide are..

negative ions containing only one element (apart from hydroxide ions which are OH-)

ionic bonding

transfer of electrons between atoms to form ions

how are ions in ionic compounds held together

a giant lattice by electrostatic forces

why do ionic compounds have high melting points

a lot of energy is needed to overcome the string electrostatic forced that hold the ions together

why can’t solid ionic compounds conduct electricity

the ions are held in fixed positions

why can melted or dissolved ionic compounds conduct electricity

the ions are free to move

how do simple molecules form

when atoms join together through covalent bonds

ionic bond

a strong electrostatic force of attraction between these oppositely charged ions

covalent bond

a shared pair of electrons between two atoms

why do simple molecular substances have low melting points

the forces between molecules are weak so not much energy is needed to overcome them

what are giant covalent structures

structures made up of lots of atoms that are all bonded to each other by strong covalent bonds

why do giant covalent structures have high melting points

lots of energy is needed to break all the strong covalent bonds that hold atoms together

metal structure

the atoms in metals are arranged in a regular pattern, they consist of giant structures because they have lots of atoms

why do metals have high melting points

large amounts of energy are needed to break the strong electrostatic forces between the metal atoms and the delocalised electrons

why are metals malleable

because in a metal the atoms are arranged in layers that can slide over each other

how do metals conduct electricity and heat

the electrons in metals are delocalised, so they aren’t bound to one atom, and are free to move around

how to calculate rfm

all the relative atomic masses of the atoms in that compound added together

empirical formula

the simplest possible whole number ratio of each element in that compound

molecular formula

the actual number of atoms of each element within the compound

how to find the molecular formula

see picture

conservation of mass

during a chemical reactions no atoms are destroyed and no atoms are created, this means there are the same number and types of atoms on each side of a reaction equation

calculating empirical formula from masses

see image

what is concentration

the amount of substance in a certain volume of a solution

formula of concentration

concentration (g dm-3) = mass of solute (g)

volume of solution (dm3)

calculating the mass of a product

see image

calculating the mass of a reactant

see image

limiting reactants

the reactant that is used up first (because it limits the amount of product that is formed), any other reactants are in excess

avogadro’s constant

6.02 × 10²³

what is a mole

one mole of any substance is the amount of that substance that contains an avogadro’s number of particles, so 6.02 × 10²³ particles (the particles could be atoms, molecules, or ions)

the mass of one mole of atoms or molecules of any substance is exactly the same number of…

grams as the rfm of the element or compound

how to work out the moles of a substance in a certain number of particles

see image

formula for moles

moles = mass

mr

how to calculate how many atoms there are in a given mass of substance

see image

balancing equations using reacting masses

see image

in solids..

strong forces of attraction between particles, the forces hold the particles close together in fixed positions to form a very regular lattice arrangement. the particles in a solid don’t have much energy so they don’t move from their positions, because of this all solids keep a definite shape and volume. the particles vibrate about their positions and as the temp increases the particles vibrate more.

in liquids..

there are weak forces of attraction between the particles. the particles are arranged randomly and are free to move past each other, but stick close together. they have a definite volume but don’t keep a definite shape. the particles in a liquid are constantly moving and the liquid gets the faster the particles move

in gases..

the forces of attraction between particles are very weak. the gas particles are free to move constantly and randomly, travelling in straight lines until they collide with another particle or the walls of the container. the particles are very far apart, so much that most of a gas is empty space. don’t have a set shape and fill the shape of the container. the hotter a gas gets the faster the particles move and causes the particles to hit the walls of the container more frequently causing pressure to increase.

state change from solid to liquid

melting

state change from liquid to gas

boiling

state change from gas to liquid

condensing

state change from liquid to solid

freezing

state change from solid to gas

sublimation

state change from gas to solid

deposition

physical change

a change in the arrangement or energy of the particles, not the particles themselves. can be undone by heating or cooling the substance

chemical changes

happen during chemical reactions, when bonds between atoms break and atoms change places. so atoms are rearranged to form different substances. unlike physics changes chemical changes are difficult to reverse

a pure substance

a substance completely made up of a single element or compound

a mixture

a substance containing more than one compound or different elements that aren’t all part of a single compound

how to test for purity

if the substance is a mixture then it will melt gradually over a range of temperatures, e.g. pure ice melts at 0°C and pure water boils at 100°C, there’s no range

simple distillation

used to separate out a liquid from a mixture, eg used in the industry to get pure water from sea water

fractional distillation

see image

filtration

see image

crystallisation

if a solid can be dissolved it is said to be soluble. you can use crystallisation to separate a soluble product from a solution

chromatography

chromatography is a method used to separate a mixture of soluble substances and identify them

Rf value

the ratio between the distance travelled by the dissolved substance (solute) and distance travelled by the solvent

how to calculate the Rf value

distance traveled by solute

distance travelled by solvent

process of water purification

filtration, sedimentation, chlorination

what is the ph scale

a measure of how acidic or alkaline a solution is, the pH scale goes from 0 to 14

pH of an acid

less than 7 (the lower the pH the more acidic)

pH of an alkali

greater than 7 (the higher the pH the more alkaline the substance is)

pH of a neutral substance

7, pure water is an example of a neutral substance

concentration of ions

The higher the concentration of hydrogen ions in a solution, the more acidic it is, so the lower the pH will be. So, as the concentration of hydrogen ions increase, the pH decreases. In alkaline solutions, the higher the concentration of OH- ions, the higher the pH