OCR 21st century science C4 topic
- Created by: Christanina
- Created on: 15-12-16 17:19
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- C4
- What is an element?
- Elements are substances that are only made with one atom
- DIfferent elements have different proton numbers
- They are arranged in order of increasing proton number in the periodic table
- Relative Atomic Mass - is the total number of protons and neutrons in an atom
- You can tell whether the element is a metal or a non metal by looking at their position in the table
- Groups
- A verticle column on the periodic table of elements is called a group
- Elements in a group have similar properties
- Group 1 for example includes elements like sodium and potassium
- Group 1 elements have one electron in their outer shell
- Group 7 elements have seven electrons in their outer shell
- Group 1
- There are 6 metals in group 1
- They're called alkali metals
- The properties of the metals alter as you go down the group
- The further an element is down the group...
- The higher the reactivity
- the lower the melting and boiling points
- the higher the density
- Trends
- Alkali metals have similar properties because they all have one electron in the outer shell
- The alkali metals get more reactive because the outer shell is further away from the nucleus
- Group 7
- These are known as halogens
- consists of 5 non metals
- They can be used for bleach dyes and kill bacteria in water
- The further down an element is down the group...
- The lower the reactivity
- the higher the melting and boiling points
- The higher the density
- They all have seven electrons in their outside of the group
- Atoms
- An atom has a small central nucleus, made up of protons and neutrons
- The nucleus is surrounded by electrons which are arranged in shells
- They have the same amount of protons as electrons
- This makes the atom neutrally charged
- A proton has the same mass as a neutron. This
- To find out the amount of neutrons you subtract the bottom number from the top number
- Balanced Equations
- The total mass of the products of a chemical reaction = the total mass of the reactants
- Chemical symbol equations must always be balanced
- 2Na + 2H2O -> 2NaOH + H2
- Ions
- Ions are atoms that gain/lose atoms
- atoms lose electron = positively charged
- Atom gains electron = negatively charged
- Ionic Bonding
- Ionic bonding occurs between a metal and a non-metal
- Compounds of group 1 and group 7 elements are called ionic compounds (salts)
- When ionic crystals dissolve in water they conduct electricity
- What is an element?
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