Atomic structure
Matter is anything which has volume and mass - basically, matter makes up everything around us.
- All matter is made up of atoms!
An atom is one particle present in every type of element. It consists of 3 subatomic particles:
Atoms have no charge because they contain the same number of protons (+ve charge) as electrons (-ve charge). |
The atomic number of an atom is simply the number of protons it has. For example, the above atom has 6 protons, therefore it's atomic number is 6. This means it is number 6 on the periodic table. The atomic number is important as it allows us to determine some of the elements properties.
The mass number is roughly double the atomic number but not always exactly - for example, aluminum has 13 protons and 14 neutrons equating to a mass number of 27.
- The mass number = number of protons + number of neutrons
The mass number is roughly double the atomic number but not always exactly - for example, aluminum has 13 protons and 14 neutrons equating to a mass number of 27.
Isotopes are atoms of the same element with the same atomic number, therefore the same number of protons, but a different mass number due to a differing number of neutrons.
For example, Carbon-14 and Carbon-12 both have 6 protons but, C-14 has 8 neutrons while C-12 has 6
Isotopes have the same chemical properties as they have the same number of valence electrons but the isotope with the higher mass number will be more dense and so their physical properties will be different.
For example, Carbon-14 and Carbon-12 both have 6 protons but, C-14 has 8 neutrons while C-12 has 6
Isotopes have the same chemical properties as they have the same number of valence electrons but the isotope with the higher mass number will be more dense and so their physical properties will be different.
On the left is C-12, the middle is C-13 and on the right is C-14
Electron configurations
Electron configurations are a description of the number of electrons in each energy level (or electron shells). They are very important as they help you determine the properties of elements.
For the first 20 elements, there is a system for arranging the electrons:
- You must fill the first shell before the second, the second before the third etc.
- The first shell holds a maximum of 2 electrons, the second, third and forth can all hold a maximum of 8 electrons
- You must always remember to use all the electrons that the element has
- Electrons are always placed in pairs as far away from each other as possible - this is because they are all negatively charged and like charges repel!
Example 1: Magnesium has 12 electrons - this means there will be 2 in the first shell, 8 in the second and 2 in the third. Thus, magnesium's electron configuration is 2,8,2
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Example 2: Calcium has 20 electrons - this means there will be 2 in the first shell, 8 in the second, 8 in the third and 2 in the fourth. Thus, calcium's electron configuration is 2,8,8,2
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Both of these elements have 2 valence electrons in their outer most energy levels, this indicates they are both found in group 2 of the periodic table and have similar properties.
The electron configuration of an element tells you what row it is in and what group it is in.
Let's take oxygen: it has 8 electrons giving it an electron configuration of 2,6. The 6 tells us it has 6 valence electrons, therefore in group 16. The electrons fill 2 energy levels which tells us it is in period 2.
Let's take oxygen: it has 8 electrons giving it an electron configuration of 2,6. The 6 tells us it has 6 valence electrons, therefore in group 16. The electrons fill 2 energy levels which tells us it is in period 2.
- Remember, groups go down, periods go across.
Ions
When an atom loses or gains electrons, an ion is formed
Atoms with 3 or less electrons in their valence shell, lose electrons to form positive ions.
Positive ions are called cations
To remember this - just look at the 't', it looks like a + sign.
- If an atom loses electrons, it is losing negative charges but it still has the same number of protons - therefore it becomes a positive ion as it has more positive charges than negative.
Positive ions are called cations
To remember this - just look at the 't', it looks like a + sign.
Atoms with 5 or more electrons in their outer energy level gain electrons when they react to form negative ions.
Negative ions are called anions
- They become negatively charged because the are gaining negative charges and now have more electrons than protons - ie. more negative charges than positive charges.
Negative ions are called anions