Chemistry Edexcel Topic 1

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What are the three ideas in John Dalton's theory about the atom

Atoms cannot be created, divided or destroyed, atoms of the same element are exactly the same and atoms of different elements are different, atoms join with other atoms to make new substances

What was Dalton's original atom model

Tiny spherical objects that cannot be divided any further

What discovery caused the original Dalton model of an atom to change

The discovery of subatomic particles

How did JJ Thompson discover the electron

He experimented using a cathode ray tube - the beam moved towards the positively charged plate so he knew that the particles must have a negative change

Describe the atomic model proposed by JJ Thompson

Plum pudding model - a positively charged ball with negatively charged electrons scattered throughout

What did Ernest Rutherford discover from his gold foil experiment

He shot a beam of positively charged particles at sheet of gold foil - most of the particles passed straight through suggesting that atoms were mostly empty space, a few particles were deflected and a few bounced directly back showing that there must be a tiny, dense and positively-charged nucleus

Describe Rutherford's new model of the atom

Mass concentrated in the central nucleus, mostly empty space, electrons travelling in random paths around the nucleus

Describe the structure of an atom

Small central nucleus made up of protons and neutrons with electrics orbiting around the nucleus in shells

What is the radius of the nucleus - how large is it compared to the radius of an atom

The radius of the nucleus is 1x10^-14m which is 1/100000 of the atomic radius

What are the relative masses of protons, neutrons and electrons

Proton: 1
Neutron: 1
Electron: 1/1836

What are the relative charges of protons, neutrons and electrons

Proton: +1
Neutron: 0
Electron: -1

Why do atoms contain equal numbers of protons and electrons

Atoms are stable with no overall charge - protons are positively charged and electrons are negatively charged and the charges in an atom are balanced so there must be an equal number of protons and electrons

Where is the mass of an atom concentrated

In the nucleus

What does the atomic number of an atom represent

The number of protons

What does the mass number of an atom mean

The mass number is the total number of protons and neutrons found in the nucleus of an atom

What do atoms of the same element contain

The same number of protons in the nucleus - the number of protons is unique to that element

What is an isotope

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons (have the same atomic number but different mass numbers)

Why is the relative atomic mass not always a whole number

Different isotopes of the same element have different mass numbers - the relative atomic mass is an average of the masses of all these isotopes

What two values would be required to calculate the relative atomic mass of chlorine

Mass numbers and relative abundances of all the isotopes of chlorine

How would you calculate the relative atomic mass of an element

(Sum of (isotope mass x abundance))/100

How did Mendeleev arrange the elements in his periodic table

Elements arranged with increasing atomic masses and elements with similar properties put into groups (due to periodic trends in chemical properties) with gaps left for undiscovered elements

How was Mendeleev able to predict the properties of new elements

He left gaps in the periodic table and used the properties of elements next to the gaps to predict the properties of undiscovered elements

Mendeleev's table lacked done accuracy on the way he ordered his elements - why was this

Isotopes were poorly understood at the time and protons and neutrons had not been discovered at that time - he thought he'd arranged the elements in order of increasing relative atomic mass but it was not always true because of the relative abundance of isotopes of some pairs of elements in the periodic table

How are elements arranged in the modern periodic table

In order of increasing atomic number, in rows called periods

What similar property do elements in the same group (column) have

Chemical properties

Why do elements in the same group (column) have similar chemical properties

They have the same number of outer shell electrons - the number of outer shell electrons determines how an atom reacts

What does the period (row) number tell you about all the elements in that period (row)

They have the same number of electron shells

What does the group number tell you about all the elements in that group

All elements in the same group have the same number of electrons in the outer shell

On which side of the periodic table are the metals positioned

On the left hand side

What determines whether an element is metal or not

The atomic structure of the element - all metals form positive ions so have 1-3 electrons in their outer shell, and non metals generally have 5-7 electrons in their outer shell

What is the maximum number of electrons allowed in each of the first 3 shells

First: 2
Second: 8
Third: 8

When are atoms most stable

When they have full electron shells

How is the electron configuration of an element related to its position in the periodic table

Number of shells is the period, number of electrons in the outer shell is the group, the total number of electrons is the atomic number

What is an ionic bond

A bond between a metal and non metal involving the transfer of electrons

How are ionic bonds formed

When an atom transfers electrons to others to produce cations and anions

In terms of electrons, describe what happens to the metal and non metal when an ionic bond forms

The metal atom loses electrons to become a positively charged cation and the non metal atom gains electrons to become a negatively charged anion

What is an ion

An atom or group of atoms with a positive or negative charge

If an ion is positively charged, has it lost or gained electrons

It has lost electrons - there are fewer negatively charged electrons to cancel out the charge of the positive protons, making the overall charge positive

Na+ has the atomic number 11 and the mass number 23 - how many protons, neutrons and electrons are in this ion

Protons - 11, electrons - 10, neutrons - 12

O2- has the atomic number 8 and the mass number 16 - how many protons, neutrons and electrons are in this ion

Protons - 8, electrons - 10, neutrons - 8

Why do elements in groups 1, 2, 6 and 7 readily form ions

They don't need to lose or gain many electrons to become more stable and gain a full outer shell so will more readily form ions to achieve a more stable structure

What type of ions do elements in group 1 and 2 form

Cations - group 1 metals will form 1+ ions and group 2 metals will form 2+ ions

What type of ions do elements in group 6 and 7 form

They are non metals so form anions - group 6 will form 2- ions and group 7 will form 1- ions

What does it mean if an ionic compound ends in -ide

The compound contains 2 elements

What does it mean if an ionic compound ends in -ate

The compound contains at least three elements, one of which is oxygen

Describe the structure of an ionic compound

Lattice structure with a regular arrangement of ions held together by strong electrostatic forces between oppositely charged ions

What is a covalent bond

A bond formed when an electron pair is shared between two non metal atoms

What forms as a result of covalent bonding

A molecule

Draw a dot and cross diagram for the formation of methane (CH4)

Are covalent bonds weak or strong

Strong

Are intermolecular forces weak or strong

Weak

Which is smaller, an atom or a molecule

An atom - simple molecules consist of atoms joined by strong covalent bonds within the molecule

Why do ionic compounds have high melting points

Strong electrostatic attraction between the positive and negative ions which requires a lot of energy to overcome

When do ionic compounds conduct electricity

When molten or in solution (aqueous)

Why can ionic compounds conduct electricity

Because the ions are charged and free to move and carry charge when the ionic compound is molten or in solution - when it is solid, the ions are fixed in a lattice structure so cannot move and carry charge

Why do simple molecular compounds have low melting and boiling points

They have weak intermolecular forces (forces between molecules) which only require a little energy to overcome

Do simple molecular compounds conduct electricity

No because there are no charged particles

Do giant covalent structures have a high melting point

Yes because they have lots of strong covalent bonds (and no intermolecular forces because there are no molecules) which require a lot of energy to break

Can giant covalent structures conduct electricity

They generally don't conduct electricity because they generally don't contain charged particles (apart from graphite and graphene)

What are giant covalent structures

Huge networks of covalently bonded non metal atoms with no intermolecular forces as there are no molecules - they can also be called giant lattices and have a fixed ratio of atoms in the overall structure

How do metals conduct electricity and heat

The positive ions are fixed in a sea of delocalised electrons which are free to move and carry charge

Are metals soluble in water

No

Name two giant covalent structures formed from carbon atoms

Graphite and diamond

Describe the structure of graphite

Each carbon atom is bonded to 3 other carbon atoms which form hexagonal rings of carbon atoms and has one delocalised electron per atom - there are many layers of carbon rings with weak intermolecular forces between layers

Describe and explain the properties of graphite

Graphite is soft and slippery because there are only weak intermolecular forces between the layers which allows the layers to slide over each other - graphite also conducts electricity because there is one delocalised electron per carbon atom which forms a sea of delocalised electrons which are free to move and carry charge

Describe the structure of diamond

All carbon atoms are covalently bonded to four other carbon atoms and there are no delocalised electrons

Describe and explain the properties of diamond

It is very hard and has a strong melting point because it contains strong covalent bonds which require a lot of energy to break, and it does not conduct electricity as there are no charged particles

Why is diamond hard and graphite soft

Graphite is soft because it has weak intermolecular forces between its layers whereas diamond has no molecules so is hard due to its giant covalent lattice and many strong covalent bonds

What are the uses of graphite

As electrodes because graphite conducts electricity and has a high melting point and as lubricant because it is slippery (the layers in graphite can slide over each other)

Why is diamond used in cutting tools

Because it's very hard

What is a fullerene

A molecule made of carbon which is shaped like a closed tube or a hollow ball

Name two fullerenes

Graphene and C60 (buckminsterfullerene)

What are the properties of the fullerene C60

Slippery due to the weak intermolecular forces, has a low melting point due to intermolecular forces, spherical, has strong covalent bonds between the carbon atoms in the molecule and has a large surface area

What are the properties of graphene

High melting point due to covalent bonding between carbon atoms and conducts electricity because it has delocalised electrons

Why is graphene useful in electronics

It is extremely strong, has delocalised electrons which are free to move and carry charge so can conduct electricity, and it is only one atom thick as it is only a single layer of graphite

What is a polymer

A long chain of molecules formed from many monomers

What are simple polymers

Simple polymers consist of large molecules containing chains of carbon atoms

Name a polymer

Polyethene

Draw the structure of polyethene

What bond is formed between carbon atoms in polymer molecules

Covalent bonds

What are the properties of metals

High melting point, high density, good conductors of electricity, malleable and ductile, and generally shiny

Explain why metals are malleable

The atoms are arranged in uniform rows which can slide over one another so are easier to bend and shape

Explain why metals can conduct electricity

The electrons in the metal are charges that can move

What are the properties of non metals

Low boiling points, poor conductors of electricity and brittle when solid

List the limitations of dot and cross diagrams when representing ionic compounds

Doesn't show a lattice structure or ionic bonds between the ions

List the limitations of 2D diagrams when representing ionic compounds

Only shows one layer of the ionic compound and doesn't show the formation of ions

List the limitations of 3D diagrams when representing ionic compounds

Shows spaces between the ions and doesn't show the charges of the ions

List the limitations of dot and cross diagrams when representing covalent molecules

Doesn't show relative sizes of atoms or intermolecular forces

List the limitations of ball and stick diagrams when representing covalent molecules

Bonds shown as sticks rather than forces and doesn't show how the covalent bonds form

How do you calculate the relative formula mass (Mr) of a compound

Add together all the relative atomic masses of the atoms in the compound

What is the empirical formula

The empirical formula is the smallest whole number ratio of the atoms of each element in a compound

What 2 values could be used to calculate the empirical formula of a simple compound

Reacting masses or percentage composition

What is the empirical formula for Fe2O4

FeO2

What is the molecular formula

The actual number of atoms of each element in a compound

Describe an experiment to work out the empirical formula of magnesium oxide

1) Weigh out a sample of magnesium
2) Heat the sample in a crucible
3) Weigh the mass of magnesium oxide at the end
4) Calculate the mass of oxygen (increase of mass)
5) Calculate the moles of magnesium and oxygen using the experimental mass and the relative atomic mass
6) Work out the whole number ratio of the number of moles of magnesium to oxygen

What is the law of conservation of mass

No matter is lost or gained during a chemical reaction

If a reaction is carried out in a closed system, what can you say about the total mass of the reaction throughout the experiment

The mass stays constant

If a reaction is carried out in an open system and a gas is produced, what can you say about the total mass of the reaction throughout the experiment

The mass decreases as the gas escapes

What equation links mass, moles and relative atomic mass

Mass = Mr x moles

How can you calculate concentration of solutions in g/dm^3

Concentration = mass/volume