Atom, element, compound and mixture

Atom, element, compound and mixture

1. All substances are made from tiny particles called atoms

2. An atom is the smallest part of an element that can exist.

   • A chemical symbol: consists of one or two letters, always starts with a capital letter, with any other letter in lower case
     • There are over 100 different elements.
     • Elements are arranged into groups with similar properties. Groups are numbered from 1 to 7, then 0.
     • A chemical formulae used to represent an element or compound in balanced chemical equations.
       • Example:Helium- He, Lithium- Li, Beryllium- Be, Boron- B, Carbon- C, Neon- Ne, Sodium- Na, Magnesium- Mg
       • Some non-metal elements exist as molecules that are made up of two atoms joined together. The formulae of these elements are the element's symbol followed by a subscripted '2'.
         • Example: Iodine- I2, Bromine- Br2, Chlorine- Cl2, Fluorine- F2, Oxygen- O2, Nitrogen- N2, Hydrogen- H2
           • Mnemonic: IBring Clay For Our New House.

3. An atom is a tiny particle that the naked eye cant see, not even a microscope

4. A compound is a substance that contains two or more elements that are chemically combined

   • Many compounds exist naturally. They can also be formed from their elements in chemical reactions. In a chemical reaction, one or more new substances are formed.
   • Example: Sodium chloride- NaCl, Potassium bromide- KBr, Magnesium iodide- MgI2, Carbon Dioxide- CO2
   • Compounds can not be seperated physicaly they have to be seperated Chemically

5. An ion is a charged particle formed when an atom, or a group of atoms, loses or gains electrons.

   • Example: Sodium-Na+- One positive, Chloride - Cl- -One negative
   • The formula of an ionic compound can be predicted using the formulae of its ions.
     • Example: Sodium chloride- NaCl - One positive, one negative , Sodium oxide- Na2O- Two positive, two negative

6. Word equations represents a chemical reaction using the names of the substances involved.

   • Word equations always take this form: reactants → products
     • There can be different numbers of reactants and products. For example: sodium + chlorine → sodium chloride

7. A balanced chemical equation represents a chemical reaction using the formulae of the reactants and products.

   • Balanced chemical equations sometimes include state symbols in brackets after each formula. They show the physical state of that substance.
     • Example: (s)- Solid
   • The law of conservation of mass states that no atoms are lost or made during a chemical reaction, so the total mass of the products is equal to the total mass of the reactants.