C1 - Atomic Structure and the Periodic Table

What is an atom?

The smallest particle of an element that can exist

What is a substance?

A substance is made up of only one type of atom

What is a compound?

A substance made up of two or more elements chemically bonded together

How can compounds be broken down into elements?

By chemical reactions

What is a mixture?

A mixture is a substance that contains two or more elements that are not chemically bonded together

What is the difference between compounds and mixtures?

• In compounds, the elements are chemically bonded together
  

• In mixtures the substances are mixed together but not chemically bonded

How can mixtures be separated?

• Filtration, crystallisation, simple/fractional distillation, chromatography

What is chromatography used for?

To separate mixtures and help identify substances

Chromatography practical

1. Use a pencil to draw a line near bottom of chromatography paper
   

2. Add a spot of ink on the line
   

3. Place a sheet of paper in the solvent (solvent must be below the paper)
   

4. Wait for the solvent to move up the paper
   

5. When solvent has reached top of the paper, take paper out and leave it to dry

What is the stationary phase?

The paper itself, as it does not move

What is the mobile phase?

The solvent, as it does move

What is filtration used for?

To separate insoluble solids from liquids

Filtration practical

1. Fold filter paper and put it in a filter funnel. Put funnel on the neck of the flask
   

2. Pour the mixture into the funnel
   

3. Allow the liquid to pass through the tiny pores in the filter paper
   Solid material cannot pass through so it is trapped
   
   Now we have our liquid separated from our solid
   

What is crystallisation used for?

To separate soluble solids from a liquid

Crystallisation practical

1. Pour 40cm³ of dilute sulfuric acid into beaker and gently heat it
   

2. Add copper oxide and stir with glass rod
   

3. Keep adding copper oxide in excess to neutralise all the acid
   

4. Pour mixture into filter paper to remove the excess copper

Continuation of crystallisation practical

5. Pour solution into an evaporating basin and gently heat over a water bath
   

6. Remove basin from heat and allow to cool (Crystals of copper sulfate form)
   

What is distillation used for?

To separate liquids from solutions

Simple Distillation Practical

1. Evaporate the liquid by heating it, which turns it into a vapour.
   

2. The vapour condenses as it passes the condensing tube, turning it back into a liquid. Liquid is collected in a beaker
   

3. Now, the salt crystals remain in the flask, and the liquid in the beaker

What did John Dalton think of atoms?

He described atoms as solid spheres

What did J.J. Thompson think of atoms?

The plum pudding model - showed the atom as a ball of positive charge with negatively charged electrons embedded

Alpha Scattering Experiment (Rutherford)

Alpha particles fired at thin sheet of gold foil

What observations were made?

1. Most alpha particles went straight through
   

2. Some were deflected slightly to the side
   

3. Some were deflected backwards

What did Rutherford conclude from this?

1. Most of the atom is empty space (particles went straight through)
   

2. The nucleus is small and positively charged (particles were deflected)
   

3. Most of the atom’s mass is concentrated in the nucleus (few particles bounced back)

What did Niels Bohr propose?

Electrons orbit the nucleus in shells – each shell is a fixed distance from the nucleus.

What did later experiments lead to?

The idea that the nucleus can be divided into smaller particles – protons

What did James Chadwick discover?

After 20 years, he discovered neutrons

What are the three subatomic particles in an atom?

Protons, neutrons, and electrons

What is the charge and relative mass of a proton?

1+ charge, mass 1

What is the charge and relative mass of a neutron?

0 charge, mass 1

What is the charge and relative mass of an electron?

-1 charge, very small mass

Why is an atom neutral overall?

As it has the same number of protons and neutrons

How big is an atom?

About 1 × 10⁻¹⁰ m

What does the atomic number tell you?

The number of protons in an atom (also number of electrons)

What does the mass number tell you?

The number of protons and neutrons

What are isotopes?

Atoms of the same element that has the same number of protons but a different number of neutrons

How do you calculate the relative atomic mass?

(Isotope abundance × isotope mass number) ÷ total abundance

How are electrons arranged in atoms?

In electron shells around the nucleus

How many shells can the first shell hold?

2 electrons

How many electrons can the second shell hold?

8 electrons

Who developed the modern periodic table?

Dmitri Mendeleev

How did Mendeleev arrange the elements?

• Mainly by atomic mass, but in some cases he did change the order because of the properties of the elements
  

• He left gaps for undiscovered elements

How is the modern periodic table arranged?

In order of increasing atomic number

What do columns (groups) represent

Elements with similar properties

What do rows represent?

Elements with the same number of electron shells

What do metals form when they react?

Positive ions

What do non-metals form when they react?

Negative ions

What are some properties of metals?

• High boiling and melting points
  

• Good conductors of heat and electricity
  

• Malleable (bent into different shapes)
  

• Shiny
  

• Strong and hard

What are some properties of non-metals?

• Poor conductors of heat and electricity
  

• Usually dull
  

• Brittle
  

• Low melting and boiling points

What are the group 1 metals known as?

Alkalis

How many electrons are in their outer shell?

1, which makes them very reactive

What type of ions do they form

1+ ions

What are the physical properties of Group 1 metals?

• Soft
  

• Low Density
  

• Low melting/boiling points

What happens as you do go down the group?

• Reactivity increases – The outer electron is further away from the nucleus as you go down the group, so it’s more easily lost
  

• Lower melting and boiling points

How do Group 1 metals react with water?

• They react very vigorously
  

• They produce hydrogen and also form hydroxides that dissolve in water (alkaline solutions)
  

• Lithium, sodium, and potassium float around surface, fizzing 

What are group 7 elements known as?

The Halogens

How many electrons are in their outer shell?

7

What type of ions do halogens form?

-1 ions

What happens as you go down the group?

• Reactivity decreases – it’s harder to gain an electron as the outer shell is further from the nucleus
  

• Boiling and melting points increase as you go down the group

What are the group 0 elements known as?

The Noble Gases

How many electrons do they have on their outer shell?

• They have 8 electrons, a full outer shell, apart from helium which has two
  

• They don’t need to gain or lose electrons, so they don’t react 
  
  

What are some properties of noble gases?

Colourless, non-flammable, and exist as monatomic gases (single atoms not bonded to each other)

What happens as you go down the group?

The boiling points increase as you go down the group

This is due to an increase of electrons leader to greater intermolecular forces between them which need to be overcome