Science Topic 2 - Matter

5.1/5.2 Atomic Structure

An atom is the smallest particle of matter

All substances are made from atoms

An element is a substance that is made by only one atom

An element cannot be broken down into simpler substances

A compound is a substance made from more than one kind of atom

In 450 BC Democritus wondered what would happen if you continuously cut an apple smaller and smaller, eventually, he decided if you cut it any smaller it would no longer be an apple. He called the 'uncuttable' 'atomos'

Antoine Laviosier made measurements of compounds and discovered that the mass of oxygen was always 2.66 times the mass of carbon, he called this 'fixed air'

John Dalton linked elements and atoms in simple ratios

JJ Thompson found positive and negative particles in atoms (Plum Pudding Model)

Ernest Rutherford used gold foil and radioactive particles to find the nucleus

Niels Bohr proposed that negative partices orbit the positive nucleus of an atom

Protons and Neutrons are located inside the nucleus whilst electrons can be found orbiting the nucleus in electron shells

Each electron shell has a different energy level

5.3 Atoms and the Periodic Table

Each element is made up of a different type of atom

The periodic table displays and organises all known elements

Each element (or type of atom) has its own square

An element symbol is a letter abbreviation used in chemistry

Each element has a unique chemical symbol

The atomic number is the smaller of the two numbers in the element square

The atomic number is equal to the number of protons in that element

Each element has a different atomic number

In a neutral (normal) atom the number of electrons will be the same as the number of protons (atomic number)

The mass number is the larger of the two numbers in the element square

The mass number is made up of the protons (atomic number) PLUS the number of neutrons

Electrons don't add to the mass of the element because they are very tiny

When writing mass numbers round up/down to the nearest whole number

The periodic table is organised in order of atomic number

The verticle columns on the periodic table are called groups

The elements in a group all react the same way

They are numbered from 1-18

The horizontal rows on the periodic table are called periods

5.4 Atoms and Ions

Electrons are located in regions called electron shells

The lowest energy shell is closest to the nucleus

Inner shells begin filling first, they are smaller and can hold fewer electrons

A maximum of 2 electrons can occupy the first shell

A maximum of 8 electrons can occupy the second shell

A maximum of 18 electrons can occupy the third shell but the fourth shell will begin to fill once the third shell contains 8 electrons

The outermost shell of an atom that contains electrons is called the valence shell and can hold a maximum of 32 in Bohrs model but 2 in the first 20 elements on the periodic table

The electrons in the valence shell are called valence electrons

If the valence shell is full, the atom is stable

Only a few elements have a full valence shell. These are called noble gasses and are located in group 18

Atoms with a full valence shell don't react or bond with any other substances, they are very stable elements and are able to exist as single atoms

Atoms of all other elements react with each other to achieve a full valence shell.

They can achieve a full valence shell by either; Giving, Taking or Sharing electrons with another atom

Atoms that have gained/lost electrons are called ions

In an ion, the number of protons is always the same but the number of electrons has changed

In a positively charged ion, there are more protons than electrons

In a negatively charged ion, there are more electrons than protons

In a neutral atom, the number of protons and electrons are the same

Cations are positive ions and tend to be metals with a metal name 

Anions are negative ions and tend to be non-metals with their name ending in ...ide

To form ions, electrons have to be either lost or gained from another atom. This is called ionic bonding

Polyatomic ions are ions that contain more than one type of atom

The names of polyatomic ions cannot be predicted from their formulas

Once atoms have exchanged electrons, the cation and anion have opposing charges so they are very strongly attached, this is called an ionic bond

Ionic compounds are compounds (more than one type of atom) that are made of atoms stuck together by ionic bonds

Ionic compounds are very common e.g. Table Salt - Sodium Chloride

When naming ionic compounds the metals are written first and the non-metals second 

When naming ionic compounds the metal name doesn't change however the non-metal does e.g. Oxygen --> Oxide

5.5 Electron Configuration

Electrons are negative particles

Electrons move around the nucleus in regions called electron shells

Electron shells correspond to the energy levels

The more energy an electron has, the further away it is from the nucleus

The energy levels are; K (Closest to Nucleus and Lowest Energy), L (2nd Lowest Energy), M (2nd Highest Energy) and N (Highest Energy)

Electron configuration is the way electrons are arranged in electron shells

Lower energy shells are filled first, moving outwards from the nucleus

Each electron has the lowest energy possible, this is called ground state and is the most stable configuration of a neutral atom

For the First 20 elements - 2 max in the first shell, 8 max in the second shell, 8 max in the third shell and 2 max in the fourth shell

Ground state is when the electrons have the lowest energy possible

Electrons can absorb energy (usually through heat), when this occurs it is called the excited state

Excited states are unstable so the high energy electrons want to get rid of that energy and return to their normal state

High energy electrons can return to their normal state by releasing the excess energy in form of light.

The colours of light released during the electrons transformation from a high state to ground state depends on the characteristics of the elements

5.6 Atoms and Isotopes

Protons and neutrons are found in the nucleus

Atoms that have the same number of protons but different numbers of neutrons are called isotopes, In other words, they have the same atomic number with a different mass number

Isotopes are different forms of the same element as they have the same atomic number

Isotopes are mainly written with the element name then the isotopes mass number e.g. Lithium-7

Almost all elements exist as two or more isotopes

On the periodic table, masses of elements aren't (usually) whole numbers, this is because of isotopes

Elements don't exist as single atoms so the periodic table shows the average mass of the isotopes of that element, this is called Relative Atomic Mass

The Mass number is the Protons plus the Neutrons, Relative Atomic Mass is the average weight of an atom of that element

5.7/5.8/5.9 Nuclear Radiation

Stable Isotopes are made up of atoms with balanced forces between nuclear particles (protons and neutrons)

Unstable Isotopes are made up of atoms with unbalanced forces between nuclear particles

Unbalanced nuclear forces in unstable isotopes are usually the result of too few or too many neutrons in the nucleus of the atom

As a result of unbalanced nuclear forces, unstable isotopes emit radiation to become more stable

Radiation is energy in the form of subatomic particles or electromagnetic particles

Radiation emitted from unstable nuclei is called nuclear radiation

The release of radiation from the nucleus of an atom is known as radioactivity, radioactive decay or nuclear decay

Most naturally occurring atoms are stable, but a small proportion are unstable

Unstable isotopes are also known as radioactive isotopes but are usually abbreviated as radioisotopes

Nuclear decay may involve the release of nuclear particles (protons and neutrons) and/or excess energy

The three main types of nuclear decay are; Alpha decay, Beta decay and Gamma decay

Alpha decay and beta decay involve the release of nuclear particles whereas gamma decay involves the release of electromagnetic waves

Alpha decay is the ejection of alpha particles from a nucleus

An alpha particle consists of two protons and two neutrons

Alpha decay results in a decrease in atomic number and mass number 

Beta decay is the ejection of beta particles from a nucleus

Beta particles consist of an electron, however, it is not an electron orbiting the nucleus. A neutron is converted into a proton and an electron

Beta decay results in an increase in the atomic number and mass number

Gamma decay is the ejection of gamma rays from a nucleus

Gamma rays are not particles but electromagnetic waves, similar to X-rays but having more energy

Gamma radiations result from the movement of protons and neutrons in a high energy nucleus

Gamma decay does not change either the atomic number or the mass number

The rate (speed) of nuclear decay is measured by a radioisotopes half-life

The half-life of a radioisotope is the time it takes for half of the atoms to undergo nuclear decay and this can range from a millisecond to a billion years

Alpha radiation is the least penetrating only being able to travel a few centimetres in air and can be stopped by a piece of paper

Beta radiation can travel a few metres in the air and can be stopped by a sheet of aluminium foil

Gamma radiation is the most penetrating being able to travel several hundred metres and requires several centimetres of lead or a thick wall of concrete to stop it.

All types of radiation are damaging to living things and the more penetrating it is, the more dangerous it is

Beta and gamma radiation can cause severe burns, sickness and mutation

Alpha radiation is relatively safe unless inhaled or ingested - then it becomes a serious health hazard

Despite this, radiation is often used in medicine (at very small doses) for medical imaging and cancer treatment, among other things