Edexcel IGCSE Chemistry Section A
Notes for section A of the edexcel IGCSE Chemistry syllabus
- Created by: Hannah Ralphs
- Created on: 12-04-11 12:02
Arrangement of Particles (1)
- The steam from 5 cubic cm will fill a bucket
- Liquids are less dense than the solids they came from
- You can move through water but you can't move through a wall
Particles in a solid are often regularly packed - they can only vibrate
In a solid - the particles have strong forces attracting them
In a liquid - the particles are mainly touching but there are some gaps
In a gas - almost no forces of attraction between the particles
Melting - when a solid is heated, the particles vibrate faster + faster until the forces are no longer strong enough to keep them together
Freezing - if a solid is cooled, the particles move more slowly until the forces of attraction are strong enough to hold them together in a solid
Arrangement of Particles (2)
Boiling - when a liquid is heated to strongly that the particles have enough energy + are moving fast enough to break all forces of attraction
Evaporation - at each temp. some particles will be moving faster than others. Some v. fast particles on the surface will have enough energy to break away to form a gas
Condensing - same concept as freezing but with liquids and gases
Sublimation - does not involve a liquid. A solid will turn directly to a gas
Diffusion
In Gases:
- Each substance particle is bouncing off endless air particles as it diffuses
- Diffusion is the spreading out of particles
- Even gases with different densities will diffuse evenly
- Some particles travel faster than others
In Liquids:
- There are only small gaps in liquids for other particles to diffuse into - this is why it is so slow
Atomic Structure
- Proton - charge: +1, mass: 1
- Neutron - charge: 0, mass: 1
- Electron - charge: -1, mass: 1/1800
- Mass is concentrated in the nucleus
- Masses and charges are relative because they are so small
- Atomic/proton number - number of protons in the nucleus
- Mass number(nucleon number) - the total number of protons and neutrons in the nucleus
- Isotopes - atoms with the same atomic number but different mass numbers i.e. same number of protons, different number of neutrons
- Radioactive Isotope - an isotope that has an unstable nucleus + gives off radiation to try to stabilise itself
- The radioactivity of Carbon-14 is used in Carbon dating
- The number of electrons = number of protons
Atomic Number, The Periodic Table and Arrangement
- Arranged in order of increasing atomic number in periodic table
- The smaller number is the atomic number
- The larger number will be the mass number, the most common isotope or the relative mass
Electron Arrangement:
- Electrons are found at large distances in shells or energy levels
- Each energy level can hold a certain number of electrons
- Low energy levels are always filled before the higher ones
- 1st shell: 2 electrons
- 2nd shell: 8 electrons
- 3rd shell: 8 electrons
Columns of the periodic table are called groups. Groups contain elements with similar properties. This is because they have the same number of electrons in their outer shell.
The Periodic Table
The number of electrons in the outer shell is the same as the group number for groups 1-7
The elements in group 0 have 8 electrons in their outer shell except helium which has 2
- Group 0 are known as noble gases - they are almost completely unreactive
- Electrons in their shells can be shown by circles with dots or crosses showing the electrons
Covalent Bonding
In any bond, particles are held together by electrical attractions between a positive charge and a negative charge
A covalent bond is a bond between two non-metals
In a covalent bond, a pair of electrons is shared between two atoms because both nuclei are attracted to the same pair of electrons
Covalent bonds are often shown with dots and crosses
e.g. Hydrogen molecules are said to be diatomic because the bond is so strong that hydrogen atoms are found joined together in pairs
Alkenes, Alkanes and Alkynes all have covalent bonds because they are made from non-metals
e.g. Nitrogen gas consists of triple bonds which are very hard to break. This is why nitrogen gas is very unreactive
Ionic (electrovalent) Bonding
Ionic bonding occurs between a metal and a non-metal
One of the atoms is is attracted to the electron pair much more strongly than the other one. The electron pair is then pulled very close to that atom, and away from the other one. In effect, one of the atoms has given it's electron to the other.
The charged particles are called ions
Ion - an atom that carries an electrical charge
Cation - carries positive charge
Anion - carries negative charge
Ionic bonding is where there has been a transfer from one atom to another to produce ions. The substance is held together by strong attractions between the positive and negative ions.
Metallic Bonding
Metallic bonding occurs between two metals. Metals have high melting points and this means that the forces holding the particles in the metal together are very strong
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