Atomic Structure_

Atomic Structure

1. Composition and Structure

   • Mixture: can be separated into simpler substances with fewer parts without a chemical reaction.
   • Compound: can be broken down into simpler compounds or its elements by using a chemical reaction.
   • Elements: are substances that cannot be broken down by a chemical reaction into simpler substances.

2. Sub-Atomic Particles

   • Sub-atomic particles have both a charge and a mass.
   • The charge of a proton is +, the charge of a neutron is neutral and the charge of an electron is -.
   • An atom has an equal number of protons and electrons therefore the charges cancel out so the atom has no overall charge.
   • The sum of the protons and neutrons is the mass number as all the mass of an atom is in the nucleus. A neutron has a mass of 1 as for a proton but an electron has a mass of almost zero.
   • The protons and neutrons are in the nucleus whereas the electrons are in shells that are around the nucleus.
   • You can show electrons as dots or crosses. The electronic configuration of an atom gives the number of electrons in each shell but each shell can hold a limited number of electrons. The 1st shell can only hold up to 2, the 2nd shell can hold up to 8 and the 3rd shell can hold up to 18 but fills up with 8 and then the 4th shell is created.
   • Elements with a similar number of electrons in the outer shell will have similar chemical properties.

3. Patterns with Elements

   • The periodic table lists all the known elements by increasing protons. It has horizontal rows called periods (amount of shells) and vertical columns called groups (amount of electrons in the outer shell).
   • The number of shells in the outer shell determins how it reacts for example, noble gases have a full outer shell so they are in group 0 and unreactive.

4. Covalent and Ionic Bonding

   • Atoms without a full outer shell are unstable therefore they react to attempt to produce a full outer shell.
   • Covalent Bonding
     • Covalent Bonding happens between two non-metals and they share electrons in order to get a full outer shell.
     • For example, in water an oxygen atom needs 2 more electrons to have a full outer shell and hydrogen needs one more. Therefore oxygen produces two covalent bonds with two hydrogen atoms in order to form a full outer shell for all of the atoms involved
   • Bonds are formed in chemical reactions.
   • Ionic Bonding
     • Ionic bonding happens between a non-metal and a metal as the metal gives electrons and a non-metal gains electrons. This means the atoms involved will become stable (have a full outer shell).
     • For example, in the ionic bonding of sodium chloride the chlorine gains an electron and the sodium looses an electron. Chlorine is now negatively charged ion and sodium is a positively charged ion. The bonds are formed because the opposite charges attract.
   • A covalent bond is represented by a line between the symbols and a double bond (where an atom shares two electrons) is represented by two lines.

5. Chemical Equations

   • To balance an equation, you need to make sure you have the same number of elements on each side of the equation. You can add larger numbers at the start of a substance but you must not change the smaller numbers as this would change the substance.
   • This is used as when you react substances none are lost unless a gas is released but the amount of atoms produced does not change.

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