Fundamental Ideas

Fundamental Ideas

1. Atoms, Elements and Compounds

   • Each element is made up of one type of atom
   • The atoms in the periodic table are arranged in columns, called groups
   • Elements in the same group usually have similar properties
   • When elements react, their atoms join with atoms of other elements
   • Compounds are formed when two or more elements combine together
   • Atoms have a tiny nucleus surrounded by electrons

2. Atomic Stucture

   • The nucleus at the center of an atom contains protons and neutrons
   • Protons = Positive Neutrons = No Charge
   • An atom has overall no charge
   • Number of electrons = Number of Protons
   • All atoms of the same element contain the same number of protons - atomic number
     • Elements are arranged in order of their atomic number in the periodic table
   • The mass number is the total number of particle in the nucleus of an atom
     • Mass number = Number of Protons + Neutrons

3. Arrangment of electrons in atoms

   • Each electron in an atom is in an energy level - represented as shells
   • Elements in the same group in the periodic table have the same number of electrons in their highest emergy ;evel
   • Shell 1 = 2 Shell 2 = 8 Shell 3 = 18
   • Group 1 elements react quickly with Water and Oxgen
   • The atoms of the unreactive noble gases (in Group) all have very stable arrangements of electrons

4. Forming Bonds

   • When different elements combine they form compounds
   • When a metal reacts with a non-metal, ions are formed
     • Metal atoms lose electrons to form positively charged ions
     • Non-metal atoms gain electrons to form negatively charged ions
     • The oppositely charged ions attract each other strongly and the compound has ionic bounds
   • The chemical formula of an ionic compound tells us the simplest ration of ions in the compound
   • When non-metals combine, their atoms share electrons to form covalent bonds and molecules are formed
   • The chemical formula molecule tells us the number of atoms that have bonded together in the molecule

5. Chemical Equations

   • In chemical reactions, the atoms in the reactants re-arrange themselves to form new substances, the products
   • Atoms are neither created nor destroyed in a chemical reaction
   • Mass of products = Mass of reactants
   • When symbol equations are written, they should always be balanced
   • The number of each type of atom should be the same on both sides of a symbol equation

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