AQA GCSE Chemistry - topic `1

atom

• smallest unit of an element

• consists of a nucleus made of protons (positive) and neutrons (neutral), surrounded by electrons (negative)

• has a radius of 0.1 nm (1×10^-11m)

more about protons, neutrons + electrons

• no of protons always equals the number of electrons, giving the atom a neutral charge.

• Protons determine the atomic number and identity of the element

• neutrons affect the isotope and stability of the atom.

• the sum of its protons and neutrons is its atomic mass

__________________________________________

Subatomic particle | Relative mass | Relative charge __________________________________________

PROTONS | 1 | +1

NEUTRONS | 1 | 0

ELECTRONS | 1/2000 | -1

James Chadwick

Scientist who provided evidence for the existence of neutrons in the nucleus of an atom.

Energy Levels

The fixed distances from the nucleus where electrons can be found, categorized into different shells.

isotopes

when atoms of the same element can have a different number of neutrons, resulting in variations of the element with different atomic masses.

conservation of mass

The principle stating that mass is neither created nor destroyed in a chemical reaction, meaning the total mass of reactants equals the total mass of products.

eletron configuration

The arrangement of electrons in an atom's energy levels, which determines its chemical properties and behavior in reactions.

giant ionic lattice

A three-dimensional structure formed by ionic compounds, where oppositely charged ions are held together by strong electrostatic forces, resulting in high melting and boiling points.

what does a group number show?

The group number indicates the number of electrons in the outer shell of an element, which influences its chemical properties and reactivity.

how many electrons can be in each shell

2 in the first shell, 8 in the second one and 8 in the third one

where are protons, neutrons and electrons found?

protons: nucleus

neutrons: nucleus

electrons: shells orbiting the nucleus

how big are atoms?

They are incredibly small and can’t be seen even with the most powerful light microscope; their radius is typically measured in nanometres and they have a radius of 0.1 nm (1×10^10m)

HISTORY OF THE ATOM (first person)

in 430 bc democritus proposed that everything on earth is made out of invisible particles called atoms

HISTORY OF THE ATOM - 2nd person

in the early 1800s, John Dalton proposed that all matter is made up of atoms, which are indivisible and indestructible. He also suggested that atoms of the same element are identical, while atoms of different elements are different. he also said that atoms were round spheres

HISTORY OF THE ATOM - 3rd person

in 1897, JJ Thompson discovered the electron and so proposed the plum pudding model, suggesting that the atom is a ball of positive charge with negative electrons embedded in it

HISTORY OF THE ATOM - 4th person/ppl

in 1911, Rutherford, Geiger + Marsden conducted the gold leaf experiment, which is an experiment where positive alpha particles are fired at a thin sheet of gold leaf. 90% of the particles went straight through but 5% were deflected and 5% were reflected. the 10% that were deflected/reflected showed us that it was due to the positive nucleus and the 90% that went through showed us how there is a lot of empty space in the atom and all the mass is concentrated in the nucleus of an atom. this led to the proposal of the nuclear model.

HISTORY OF THE ATOM - 5th person

in 1913, Niels Bohr suggested that electrons orbit the nucleus at fixed distances, similar to planets around the sun. This model introduced quantized energy levels for electrons.

HISTORY OF THE ATOM - last person

in 1932, james chadwick discovered the neutron and stated that it resided in the nucleus and contributed to the mass, thus copmpleting the model as we know it today.

what happens when atoms form ions

they get a full outer shell of electrons, making them more stable and their electronic configuration becomes the same as that of the nearest noble gas

patterns in forming ions

metals form positive ions because they lose electrons

non-metals form negative ions because they gain electrons

group 4 + 8 elements when it comes to ionic bonding

most group 4 elements dont form ions but bond covalently instead

group 8 elements dont bond ionically as they alr have a full outer shell

what 2 substances does ionic bonding happen between

metals and non-metals

what is a GIL

a giant ionic lattice is a really big formation of ions held together by strong electrostatic forces (requiring lots of heat to break) in a repeating three-dimensional arrangement.

+ and - of dot a dot and cross diagram

+ = shows electron structure of ions

- = gives impression that structure is made of pairs of ions

2d space + & -

+ = easy to draw

- = only 2d, limited to only a few ions

ball and stick + & -

+ = ions are arranged relative to each other

- = may make you think there are bonds between ions

giant metallic structures

a repeating pattern of positive metal ions and delocalised electrons held together by strong electrostatic forces of attraction between the positive metal ions and delocalised electrons extending in all directions

what does the word delocalised mean in terms of electrons

delocalised means that an electron is free to move through the structure and can carry charge. the ones that become delocalised are the ones on the outer shell

giant metallic structures have a ____ MP and BP

high, as lots of energy is required to overcome the strong electrostatic forces of attraction between the positive metal ions and delocalised electrons

giant metallic structures are ____ conductors

metals are good conductors of electricity as the delocalised electrons are free to move through the structure and carry charge.

malleability, ductility and sonority

metals are malleable and ductile due to the ability of layers of metal atoms to slide over one another without breaking the metallic bond. they are also sonorous, meaning they ring when hit

radius of a nucleus

1 × 10^-14m