Atoms and Elements

Atoms and Elements

1. Atoms have a small nucleus surrounded by electrons.

   • The Nuclear model
     • The nucleus is in the middle of the atom, it contains protons of neutrons. protons are positively charged. neutrons have no charge, so the nucleus has a positive charge overall. Size wise its tiny.
     • The electrons move around the nucleus; they're negatively charged. they're tiny but they cover a lot of space. They occupy shells around the nucleus.
   • The number of protons equal the number of electrons
     • Atoms have no charge overall; they are netural. they charge on the electrons is the same size as the charge on the protons but opposite. This means the number of protons always equals the number of electrons in the atoms
   • Elements consist of one type of atoms only
     • Atoms can have different numbers of protoons, neutrons and electrons. Its the number of protons in a nucleus that decides what type of atom it is. An atom with one protons in it's nucleus is hydrogen. If a substance contains one type of atom it's called an element so all atoms of a particular element have the same number of protons and different elements have atoms with different numbers of protons.

2. The Periodic Table

   • Atoms can be represented by symbol
     • EG- C= Carbon, O= Oxygen Mg= Magnesium
     • Na= Sodium, Fe= Iron, Pb= lead
   • The Periodic Table puts elements with similar properties together
     • The Periodic table is laid out so that elements with the same properties form columns. these vertical columns are called groups. All the elements in a group have the same number of electrons in the outer shell. This is why elements in the same group have similar properties. So if you know the properties of one element, you can predict the properties of the other elements in that group
       • For example, in group 1 the elements are Li, Na, K, Rb, Cs and Fr. They are all metals and they all react with oxygen to form oxide. All the elements in group 0 are noble gases so they don't react with anything because they have a full outer shell (apart for helium)
   • The top number is the mass number. This is the total number of protons and neutrons. The bottom is the atomic number which is the number of protons.

3. Electron Shells

   • Electro Shell Ruls
     • Electrons always occupy shells (energy levels). The lowest energy levels are always filled first; these are the ones closest to the nucleus. Only a certain number of electros are allowed, 1st-2 2nd- 8 3rd- 8. Atoms are happier when they have full electron shells like noble gases. In most atoms the outer shell isn't full that's why they react to fill it
     • You need to know the electronic structures for the first 20 elements. Eg Nitrogen has 7 protons so it must have 7 electrons. the first shell can only have 2 electrons and the second maximum of 8
       • See notes for table

4. Compounds- Atoms form together to make compounds

   • When different element react, atoms form chemical bonds with other atoms to form compounds.