C1 - particles

Question 1

what do states of matter depend on?

Answer 1

forces between particles

Question 2

what are some features of a solid?

Answer 2

1. there are strong forces of attraction between particles, this holds them in fixed positions in a very regular lattice arrangement
2. the particles don’t move from their positions; all solids keep a definite shape and volume and don’t flow like liquids
3. the particles vibrate about their positions- the hotter the solid becomes, the more they vibrate (this causes solids to expand slightly when heated)
4. if you heat the solid, eventually it will melt and become liquid

Question 3

what are some features of a liquid?

Answer 3

1. there is some force of attraction between particles- they’re free to move past each other but tend to stick together
2. liquids don’t keep a definite shape and will flow to fill the bottom of a container, but they do keep the same volume
3. the particles are constantly moving with random motion; the hotter the liquid gets, the faster they move (this causes liquids to expand slightly when heated)
4. if you cool a liquid it will freeze and become solid, if you heat a liquid enough it evaporates/boils and becomes a gas

Question 4

what are some features of gases?

Answer 4

1. there’s almost no force of attraction between particles- they’re free to move and travel in straight lines (only interacting when collisions occur)
2. gases don’t keep a definite shape or volume and they can always fill any container; when particles bounce off of the walls of a container, they exert a pressure on the walls
3. the particles move constantly with random motion; the hotter the gas gets, the faster they move
4. gases either expand when heated or their pressure increases
5. if you cool a gas, it will condense and become a liquid

Question 5

what effect do chemical reactions have on atoms?

Answer 5

atoms are rearranged during chemical reactions

Question 6

what is a physical change?

Answer 6

when a substance changes from one state of matter to another (e.g. by melting, boiling, condensing or freezing), its a physical change- no new substances are formed, the original chemicals just change state

Question 7

what happens during a chemical reaction?

Answer 7

during a chemical reaction, bonds between atoms break and the atoms change places- the atoms from the substances you start off with(the reactants) rearrange themselves to form different chemicals, these new chemicals are called the products

Question 8

what is a key difference between physical changes and chemical changes?

Answer 8

compared to physical changes, chemical changes are often hard to reverse

Question 9

what did John Dalton do?

Answer 9

at the start of the 19th century, he described atoms as solid spheres and said that different spheres made up the different elements

Question 10

what did J J Thomson conclude in 1897?

Answer 10

he concluded that atoms weren’t solid spheres; his measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles (electrons)- this meant that the ‘solid sphere’ idea of atomic structure needed to be changed, the new theory was known as the ‘plum pudding model’

Question 11

what did Rutherford do in 1909?

Answer 11

in 1909, Ernest Rutherford and his students, Hans Geiger and Ernest Marsden, conducted the gold foil experiment

Question 12

what did the gold foil experiment involve?

Answer 12

positively charged alpha particles were fired at an extremely thin sheet of gold

Question 13

what was the result of the gold foil experiment?

Answer 13

from the plum pudding model, the scientists expected the particles to pass straight through the sheet or be slightly deflected at most, this was because the positive charge or each atom was though to be very spread out through the pudding’ of the atom- however, whilst most particles did go straight through the gold sheet, some were deflected more than expected and a few were deflected backwards (so the plum pudding model couldn’t be correct)

Question 14

what theory did Rutherford develop as a result of the gold foil experiment?

Answer 14

Rutherford came up with the theory of the nuclear atom to explain his new evidence- in this, there’s a tiny, positively charged nucleus at the centre, surrounded red by a ‘cloud’ of negative electrons; most of the atom’s empty space

Question 15

what did scientists realise was wrong with Rutherford’s nuclear atom?

Answer 15

scientists realised that electrons in a ‘cloud’ around the nucleus of an atom, as Rutherford had described, would be attracted to the nucleus, causing the atom to collapse

Question 16

what did Niels Bohr do?

Answer 16

Bohr proposed a new model of the atom where all the electrons were contained in shells; he suggested that electrons can only exist in fixed orbits, or shells and not anywhere in between- and that each shell has a fixed energy

Question 17

what did Bohr’s theory do?

Answer 17

Bohr’s theory of atomic structure was supported by many experiments and it helped to explain lots of other scientists’ observations at the time, it was pretty close to our currently accepted version of the atom

Question 18

what is the atom made up of?

Answer 18

protons, neutrons and electrons

Question 19

what is the relative mass and relative charge of the proton?

Answer 19

relative mass: 1
relative charge: +1

Question 20

what is the relative mass and relative charge of the neutron?

Answer 20

relative mass: 1
relative charge: 0

Question 21

what is the relative mass and relative charge of the electron?

Answer 21

relative mass: 0.0005
relative charge: -1

Question 22

what are some features of the nucleus?

Answer 22

1. the nucleus is in the middle of the atom
2. it contains protons and neutrons
3. it has a positive charge due to the protons
4. almost the whole mass of the atom is concentrated in the nucleus
5. compared to the overall size of the atom, the nucleus is tiny

Question 23

what are some features of electrons?

Answer 23

1. electrons move around the nucleus in electron shells (or orbitals)
2. they’re negatively charged
3. there tiny, but their orbitals cover a lot of space
4. the volume of their orbitals determines the size of the atom- atoms have a radius of about 10^-10 m
5. they have virtually no mass- its often taken as 0

Question 24

what are molecules?

Answer 24

• molecules are made up of two or more atoms
• they can be made up of the same element or different elements
• simple molecules, like atoms, are pretty tiny; the bonds that form between these molecules are generally a similar length to the atomic radius- about 10^-10m
• nanoparticles are a bit bigger than simple molecules (they’re typically made of around 100 atoms and range from 1nm to 100nm in size

Question 25

what does the mass number tell you?

Answer 25

the total number of protons and neutrons

Question 26

what does the atomic number tell you?

Answer 26

the number of protons

Question 27

what does the number of protons tell you?

Answer 27

atoms of the same element all have the same number of protons, so atoms of different elements will have different numbers of protons

Question 28

how would you work out the number of neutrons?

Answer 28

subtract the atomic number from the mass number

Question 29

what charge have neutral atoms got?

Answer 29

neutral atoms have no charge since they have the same number or protons and electrons (so the number of electrons in a neutral atom is also equal to the atomic number)

Question 30

how do ions form?

Answer 30

ions form when atoms gain or lose electrons; negative ions form when atoms gain electrons, positive ions form when atoms lose electrons

Question 31

what are isotopes?

Answer 31

isotopes are different forms of the same element, which have the same number of protons but a different number of neutrons