AQA Chemistry - Atomic structure and the periodic table

what are all substances made up of

Atoms

what is an atom

the smallest part of an element that can exist

how can compounds be separated into elements?

by chemical reactions

what happens in a chemicsl reaction

atoms are rearranged to form new substances, usually accompanied by an energy change

chemical reaction

a process that forms new substances, and cannot easily be undone

molecule

any elements chemically combined, even if they are the same element

compound

2 or more different elements chemically bonded together in fixed proportions

what is a feature of an element?

It cannot be broken down into anything simpler

element

a pure substance made up of only one type of atom

How are compounds formed

from elements by chemical reactions

How many different elements are there?

about 100

what is meant by the term ‘fixed proportions’

where every sample of the compound has its elements in the same ratio

balance this equation Na + Cl2 → NaCl

2Na + Cl2 → 2NaCl

make this chemical equation balanced : H2 + O2 → H2O

2H2 + O2 → 2H2O

mixtures

2 or more elements or compounds that are not chemically combined together- each substance in the micture keeps its chemical properties

what are some examples of mixtures

salt solution, air, sandy water

insoluble

a solid that does not dissolve in a specific liquid solvent, even after thorough mixing

filtration

separates an insoluble solid from a liquid

what does filtering do

separates mixtures based on the size of particles

what is number 1

filter paper

what is number 2

residue

What is number 3

filter funnnel

what is number 4

filtrate

what does crystalisation do?

separates a soluble solid from a solvent

what is Na2O

sodium oxide

periods of the periodic table

horizontal rows

groups of the periodic table

vertical columns

group 1 in the periodic table

very reactive metals

electron

a subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons

what does amu stand for

atomic mass unit

neutrons

particles with no charge that are contained in the nucleus of an atom

How many electrons can the first shell hold?

2

How many electrons can the third shell hold for the first 20 elements?

8

How many electrons does the second shell hold?

8

energy levels

The fixed regions around the nucleus where electrons are found. Electrons in shells further from the nucleus have more energy. Electrons fill the shells closest to the nucleus first.

what is the mass of a neutron

1 amu

what is the mass of a proton

1 amu

protons

positively charged particles that are contained in the nucleus of the atom

how much does an electron weigh?

It’s mass is nearly 0

what does an electron do ?

spin around the positive centre of the atom in energy levels

subatomic particle

a particle smaller than an atom

what are atoms made of

electrons, protons, and neutrons

group 0

a group of very unreactivive non- metals

group 7 in the periodic table

a group of very reactive non-metals

product

the new substance(s) formed in a chemical reaction

How do we know which period an element is in

The number of notations in the electronic configuration tells us the number of occupied shells

when are atoms more stable?

When they completely fill the outermost shell

what is the outermost shell of an atom called?

the valence shell

How do we separate a compound back into its elements?

through a chemical reaction

what do we use if we want to separate a mixture?

we use a physical separation technique

what is meant by ‘fixed proportions’

where the specific ratio of different elements in a compound remains constant

How do compounds differ from their constituent elements?

they usually have different properties from the elements that they are made from

what are the physical techniques that can be used to separate mixtures

chromotography, distillation, filtration, crystallisation

what is the relationship between molecules and compounds

all compounds are molecules but not all molecules are compounds

How are compounds presented?

by using chemical formulas that combine element symbols and numbers to show the exact ratio of different atoms

what is a chemical formula

a combination of symbols that indicates the chemical composition of a substance

what is an ion

an electrically charged particle, formed when an atom or molecule gains or loses electrons

How are ions formed?

when atoms gain or lose electrons

why would an atom gain or lose electrons

to have a full outer shell, so that they are more stable

what does the group number tell us?

How many electrons the atoms of that group have in the outermost shell

what does losing and gaining electrons need?

energy

which atoms are more likely to lose or gain electrons?

the atoms that only need to lose or gain 1 or 2 electrons

which groups can become ions easily

1, 2, 6, 7

how are ionic compounds formed?

when metals react with non metals

What are ions

atoms with a charge

isotopes

forms of the same chemical element that have the same number of protons but a different number of neutrons in their nuclei

what does the atomic number tell us

the number of protons

what is the relationship between atoms and elements

atoms are the particles that make up an element. An element is a type of atom

what is an element defined by?

the number of protons

what is the radius of an atom

around 0.1nm

when is an atom neutral

when the protons and electrons are the same

what does the mass number tell us

the total number of neutrons and protons

How do we find out the number of neutrons

mass number - atomic number

what is the formula for sodium chloride

Na₂O

element

a substance containing only one type of atom

compound

a substance containing 2 or more different types of atoms chemically bonded

why do we need to balance equations?

because of the conservation of mass- atoms cannot be created or destroyed

mixture

consists of different substances not chemically bonded together

what does filtration do?

removes large, insoluble particles from a liquid e.g sand from water

what does evaporation do?

leaves behind crystals of a dissolved solute if heated gently

what is distillation?

involves condensing the evaporated solvent and collecting it

What did John Dalton describe an atom as?

solid spheres and said that different spheres made up the different elements

Who went against John Dalton’s thoughts of atoms being a sphere?

J J Thomson

What did J J Thomson conclude about atoms?

His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles- electrons. His new theory was known as the ‘plum pudding model’

What did the plum pudding model show?

the atom as a ball of positive charge with electrons stuck in it

When did John Dalton think of atoms as solid spheres

At the start of the 19th century

When did J J Thomas conclude that atoms were not solid spheres?

in 1897

What did Ernest Rutherford discover?

that the nucleus was small and positively charged by finding that most alpha particles went straight through a gold ‘leaf’; very few deflected back

What did Ernest Rutherford do?

He and his student Ernest MArsden conducted the famous alpha particle scattering experiments. They fired positively charged alpha particles at an extremely thin sheet of gold.

How did Ernest Rutherford find out the plum model method couldn’t be right?

When conducting their experiment thet expected the particles to pass straight through the sheet, or to be slightly deflected. However, some particles were deflected more than expected, with a small number deflected backwards. So the plum pudding method couldn’t be right

Why was it assumed that rhe particles would pass straight through when Ernest Rutherfood conducted his experiment?

Because the positive charges were thought to be spread out throught he pudding of the atom.

What was Rutherford’s conclusion?

he came up with an idea to explain the nuclear model of the atom. In this, there’s a tiny positive charged nucleus at the centre, and a cloud of negatively charge electrons surrounding the nucleus

What did Niels Bohr deduce?

that electrons were contained in shells and orbit the nucleus. This was supported by many experiments

How was the periodic table made?

Before, they were put in order of their Atomic weight, some were then grouped otgether if they had similar properties. Dmitri Mendeleev grouped elements together based on their properties, and saw that there were some gaps. He concluded that these elements were yet to be discovered and he was right

How do we do filtration?

We put the mixture of the solid and the liquid into filtration paper. The fibres of the paper have gaps that water can pass through. The water that passes through is called the filtrate, and the insoluble solid stays inside the filter paper

What is A ?

residue

What is B?

funnel

what is d ?

filter paper

What is C?

conical flask

WHat are the methods that can be used to separate a mixture of elements?

Filtration, Distillation, Chromotography, Separating funnel, Fractional distillation, Crystallisation