Atomic structure and the periodic table

What is a element?

A pure substance where all the atoms are the same

What is a compound? What are features of compounds?

Compounds contain two or more different elements chemically combined in fixed proportions

• Compounds usually have different properties from the elements they are made from

• Have to use a chemical reaction to seperate compounds

What is a fixed proportion?

For every one atom of a element, we have one atom of another element

What is a mixture?

A mixture has different elements or compounds that are not chemicaly combined

• Have to use a physical seperation technique to seperate a mixture

What is a molecule?

Has any elements chemically combined even if its the same element (has a little number next to it)

What does insoluable mean?

The solid will not dissolve in liquids

What does soluable mean?

The solid will dissolve in liquids

What are the state symbols?

Tells us the physical state of a chemical

(s) = solid

(l) = liquid

(g) = gas

(aq) = dissolved in water

Filtration

Used to seperate a insoluable solid from a liquid

A physical seperation technique

• Use a filter funnel and filter paper in a conical flask

• Pour the mixture into the funnel paper

• The liquid will passes through the pores in the filter paper

• The solid material can not pass through the filter paper

The liquid that passes through is called the ‘filtrate’

Crystallisation

Used to seperate soluable solids from a liquid

A physical seperation technique

• Leave the mixture out for a few days so the liquid evaporates, leaving behind the solid

• This process can be sped up by gently heating the liquid so evaporation occurs faster

• However, certain chemicals can be broken down if heated so you have to be careful

Simple distillation

Used to seperate a dissolved solid from a liquid while keeping the liquid

A physical seperation technique

• Evaporate the liquid by heating which turns the liquid into a vapour

• Then condense the vapour back to a liquid by cooling

Steps to carry this out:

• Place our mixture into the flask and allow evaporation to occur by heating

• vapour runs up the tube into the condenser, which has cold water running in and out of it keeping the tube cold

• The vapour forms back ino the liquid due to the cooling

• At the end the original flask contains the solid and the liquid in the beaker

Can be used to convert sea water into drinking water

Fractional distillation

Used to seperate a liquids

Must have different boiling points

A physical seperation technique

• Contains a fractionating column which contains hundreds of glass beads

• When the liquids begin to evaporate, the vapours begin to mix together

• When they reach the fractionating column which is cool at the top, the vapours condense and drip back into the flask where the liquids evaporate again

• This repeated evaporation and condensation increases the amount of the lower boiling point chemical in the fractionating column

• This means that a mixture of the vapours which contains more of the mixture of the lower boiling point goes to the condenser and turns back into a liquid

REVISE OVER SEPERATELY!!!

Paper chromatography

Allows us to seperate based on their different solubilities

A physical seperation technique

• Take a piece of chromatography paper and draw a pencil line (pen would dissolve) near the bottom of the paper

• Put a dot of the first mixture on the colour line

• Place the bottom of the paper into a solvent (a liquid that will disolve substances)

• The solvent makes its way up the paper and the mixture is dissolved

• The mixture is carried up the paper by the solvent

A pure compound will leave a single spot

A mixture will seperate into different spots

What is the stationary phase in paper chromatography?

The paper as it does not move

A less soluble substance is more attracted to the stationary phase

What is the mobile phase in paper chromatography?

The solvent as it moves

A more soluble substance is more attracted to the mobile phase

What are the features of physical seperation techniques?

• No new substances made

• Does not involve chemical reactions

What was the plum pudding model?

An atom is a ball of positive charge with negative electrons embedded in it

How was the alpha scattering experiment carried out?

A experiment to test if the plum pudding model was accurate

• Scientist used a piece of thin, gold foil and fired alpha particles (positive charge) at it

What were the results of the alpha scattering experiment?

• Some alpha particles passed straight through the gold foil without changing direction

  • Told scientist atoms are mainly empty space

• Some alpha particles deflected as it passed through the gold foil

  • The centre of the atom must have a positive charge as they positive alpha particles and centre of the atom repelled

• Some alpha particles bounced off the foil

  • The centre of the atom contains a lot of mass

What was the nuclear model?

A new model of atoms

• Has a positive nucleus which contains most of the mass

• Empty space

• Negative electrons surrounding it

What are the features of the nuclear model after modifiaction?

• Mainly empty space

• Has a positive nucleus due to containing postive protons and neutral neutrons

• Around the edge of the atom, there are shells/energy levels contains electrons (2,8,8)

Name the sizes of the parts of the nuclues

• Radius of an atom = 1×10^-14m

• Radius of the nucleus = 1×10^-14m

What are the relative charges of protons, neutrons and electrons?

Protons = +1

Neutron = 0

Electron = -1

This means there is no overall charge in atoms as 1+0+-1=0

What are the relative mass of protons, neutrons and electrons?

Protons = 1

Neutrons = 1

Electrons = very small

What is the atomic number and mass number?

7 → mass number → 7 protons and neutrons

To work out the number of neutrons = 7-3=4 neutrons 0

Li

3 → atomic number → 3 protons and 3 electrons (same number of each on atoms)

What is a isotope?

Atoms of the same element with different numbers of neutrons

What are ions?

Atoms which have an overall charge

This is because ions have lost or gained ions

What do positive or negative ions gain?

Electrons are negative

Positive ions have gained electrons

Negative ions have lost electrons

Examples of negative and positive ions

23 = 23-11 = 12 neutrons

Na⁺ - lost one electron

11 = 11 protons and 11-1=10 electrons

19 = 19-9=10 neutrons

F^- - gained one electron

9 = 9 protons and 9+1=10 electrons

How do we decide what mass number for elements are put into the periodic table when their are isotopes?

We take the average of the mass numbers of each isotope but the average is weighted for abundant (how common) each isotope are

How to calculate the relative atomic mass

Relative atomic mass=

(mass number of isotope 1 x percent abundance of isotope 1) +

(mass number of isotope 2 x percent abundance of isotope 2)

/100

How do electron energy levels work?

Look at the atomic number to see the number of electrons

This shows the number of shells and elctrons in each

Up to 2 in the first shell, up to 8 in the next shells after

What does the number of electrons on the outer shell tell us?

This tells us the group the element is

Boron has 3 in the outer shell so is in group 3

A full shell of electrons means its in group 0 (the noble gasses)

What did Mendeleev do?

Developed the first modern periodic table

He arranged the elements in order of increasing atomic weight as the atomic number hadnt been discovered yet

He then switched the orders of specific elements so they fitted the paterns of other elements in the same group and left gaps in the periodic table where he thought an element was missing

What differences were made to Mendeleevs periodic table?

Elements are arranged in order of the atomic number meaning every element is in the correct group

Ordering them by atomic mass didnt work due to isotopes

Has group 0 added as these had not been fully discovered during mendeleevs time

What impacts the atoms overall charge?

• Electrons and protons have the same number of each in atoms

• If we take away electrons, they no longer cancel eachother out, changing the overall charge

• Metals always from positive ions

Eg Li₃⁷ original atoms canceled eachother out +3-3=0 but after taking away a electron it becomes +3-2=+1 which make its overall charge change to +1

What are the features of the noble gasses (group 0)?

• The noble gasses are very unreactive elements

  • They are unreactive as the atoms are stable due to full outer shells and will not react

• As we move down group 0, the boiling point increases as the atomic mass also increases

What are features of metals?

• Found on the left (the highly reactive metals) and centre (the transition metals) of the periodic table

• When metals react, they lose electrons in their outer shell to achieve a full outer energy level which gives them a stable electronic structure

• Eg aluminium loses three to become stable

What are the features of group 1 metals (alkali metals)?

• Always have one electron in their outer shell which is lost during a reaction to become stable

• Group 1 metals are soft

• Group 1 metals react rapidly with oxygen and create metal oxide

• Group 1 metals also react rapidly with chlorine

• As we move down group 1, the react more rapidly

What happens when group 1 metals react with oxygen?

• Group 1 metals react rapidly with oxygen and create metal oxide

• When a group 1 metal reacts with oxygen, the metals has one electron in its outer shell which transfers to the oxygens outer shell which has 6 electrons, making the metals atom stable

• The oxygen atom still requires a electron to stable out its outer shell, so another lithium atom also transfers its electrons to the oxygen atom, stabilising all three elements

• This changes the overall charges for each element

What happens when group 1 metals react with oxygen?

• Reacts rapidly with water and creates alkaline solutions

• This creates metal hydroxide + hydrogen

Why do the group one metals get more reactive going down the group?

When certian elements react, they can loose their outer electrons more easily making them more reactive

• This is because as the radius of the atoms increase, that means there is a greater distance between the positive nuclues and negative outer electrons which means the electron is less attracted to the nucleus

• The outer electron is also repelled by electrons in the internal energy levels as negative + negative repel which decreases the attraction between the electron and nucleus is called shielding

What happens when group 7 non-metals react with eachother (the halogens)?

• Have 7 electrons in the outer shell

• When two group 7 elements react with eachother, they form together to make a covalent bond as they over lap and share a pair of electrons

• This creates F₂ and F-F

What is a covalent bond?

A chemical bond formed when two non-metal atoms share a pair of electrons

This can be represented with a stick between two atoms eg Cl-Cl

How do we use the boiling point and melting points in group 7 to find the physical state of the elements at room temperature?

• Fluorine and chlorine are both gases at room temperature as their boiling points are lower the 20’c

• Bromine is a liquid as it has a meling point lower then 20’c and the boiling point is higher then 20’c

• Iodine is a solid at room temperature because both the melting point and boiling point is higher then 20’c

What is the relative molecular mass? How does it change going down group 7?

The relative molecular mass gives us the idea of the size of the molecule

The relative molecular mass increases (molecules get bigger)

What happens when halogens react with metals?

They form ionic compounds

The halogen gains one electron from the metal atom and froms a ion with -1 charge

This means the metals now have ‘ide’ at the end of the each element name eg bromide when it becomes a ion

The reactivity of the halogens

The halogens get less reactive moving down the group as it is harder to gain electrons

This is because going down the group there is a greater distance between the outer energy level and nuclues which means the electrons are less attracted to the nuclues

There are also more internal energy levels going down the group meaing they repel the outer electron

Describe the displacement in halogens

A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt

Eg

Sodium bromide dissolved in water (aqueous solution) + fluorine

bromide is less reactive so fluroien displaces it

→ sodium fluoride + bromine