Chemistry

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  • Created by: Emma
  • Created on: 16-05-11 14:25

Atomic Structutre

In the middle of a atom there is a small nucleus, In this nucleus there is a protons and neutrons. Surrounding the nucleus there are shells which contain electrons. Any atom has the same number of electrons orbiting its nucleus as it has protons.

Protons are Positive  (relative) charged

Electrons are Negative (relative) charged

Neutrons are Neutral (relative) charged

Atomic Number : We call the number of protons in the nucleus of an atom its atomic number or proton number. (For example the atomic number for Hydrogen is 1 and has 1 proton in the nucleus)

Each element has its own atomic number. If you are told the atomic number of an element such as 8, it would be the bottom number which after looking on the periodic table its OXYGEN

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The arrangement of electrons in atoms

Around the nucleus there are circles or also known as shells. Each shell represents a different energy level. The lowest energy is shown by it being the closest to the nucleus.

With their negative charge, electrons are attracted to the positively charged nucleus.  On the first shell the max electrons is 2, no more are allowed on the first circle, although for the rest of the shell the maximum amount is 8.

If you look at the peridoric Table and pick on element, if you count what column it is that will tell how many electrons will be on the outer shell. For example Oxygen is in group 6 so there will be 2 on the inner shell and 6 on the outer.

Elements that have a full outer shell (energy level) are very stable and UNreactive. They are called NOBLE GASES (helium/neon/argon for example)

You can also write the electrons like this (For Sodium) 2,8,1 - 2 on the first shell, 8 on the second and 1 on the last. This is not a stable element without a reaction.

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Chemical Bonding

We already know that we can mix 2 substances together without either of them changing. (We can mix salt and sand together and then separate them again and no change will happen) But in chemical reactions it’s completely different.

When 2 or more atoms react they will become compounds. The compound is formed is different to both of them and we cannot get either of them elements back easily. We can also react compounds together to form other compounds.

Why do atoms react? When an atom has a full outer shell it is stable and uncreative (like the noble gases that are in group). although most atoms don't have a full outer shell but you can make them by doing bonding. These 2 bonds are called:

·       Covalent Bonding (Includes sharing electrons between elements)

·       Ionic Bonding ( Includes Giving or receiving a electron between elements)

These bonds may include more than 2 elements.

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Ionic Bonding

Ionic bonding normally occurs when metals react with non-metals. The ions that are formed are held to each other by very strong forces of attraction between the oppositely charged ions. The ionic bonds between the charged particles results in an arrangement of ions that we call a giant structure. The giant structure of ionic compounds is very regular. This is because the ions all pack together neatly.

Ionic bonding involves a element either giving electron/s away or receiving them. If a element loses electrons they would then have a + outside the brackets and if they receive electrons it would have a - on the outside of the brackets. Just think they don’t want anymore and when they give them away they are happy (positive) and when they get more they are unhappy and get in a (negative) mood.

Outside the bracket along with the negative or positive sign you must put how many electrons were given away or given to the element. If you forget this you may lose a few marks which could be and for a very simple thing to do for the question

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Convalent Bonding

This bond happens when 2 non-metals react and they share electron between the elements so they can have a full outer shell. For example H20 - would have a oxygen in the middle and 2 hydrogen’s connected to it and sharing 4 electrons all together. This way the 2 hydrogen’s have a full outer shell and so does the Oxygen.

Giant Structures  - Many substances containing covalent bonds consist on SMALL molecules for example H2O (should be a little 2) although many structures are different. Instead they have giant structures where huge numbers of atoms are held together by a network of covalent Bonds.

DIAMONDS have a giant covalent structure. In the diamond each carbon atom forms FOUR covalent bonds with its neighbour in a rigid giant covalent lattice.

If you can’t remember the difference between Covalent and Ionic just remember

SHARING is CARING (C begins with Covalent obviously)

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Bonding in Metals

Metals are another example of giant structures. You can think of metal as a lattice of a metal atoms (or even positively charged ions), arranged in regular layers. The electrons that are on the outer shell (highest energy level) can easily move to another atom. The outer electrons form a 'sea' of free electrons surrounding positively charged metal ions.

Strong electrostatic attraction between the negatively charged electrons and positively charged ions bond the metal ions together. The electrons act a bit like glue.The 'sea' of free electrons are called delocalised electrons. These electrons help us explain the properties of metals.

Metal Crystals - The giant structure of a metal is not usually the same all through the metal. Sometimes you are able to see the metal crystals on the surface of steels that has been dipped in zinc to prevent it from rusting, We call this treatment GALVANISING.

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Questions On Chapter One

Questions (1.1-1.6)

  • What are the names of the three particles that make up an atom?
  • An oxygen has 8 protons - How many electrons does it have?
  • Which element has an atomic number of 14
  • What do you notice about the atomic numbers going from helium to neon to argon?
  • Where are the electrons in an atom?
  • Which shell represents the lowest energy level in an atom?
  • How many electrons can the first energy level hold?
  • What is the difference between mixing 2 substances and reacting them?
  • When atoms join together by sharing electrons, what type of bond is this?
  • When atoms join together as a result of gaining or losing electrons, what type of bond is this?
  • What name do we give to the arrangement of ions in an ionic compound?
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Answers

Answers to following Page:

  • Protons, Electrons and Neutrons
  • It has 8 electrons
  • Silicon
  • They are increasing
  • In the shells (energy levels) surrounding the nucleus
  • The first shell
  • 2 electrons only
  • You can undo a mixing and it will not change the 2 objects unlike Reacting
  • Covalent Bonding
  • ionic Bonding
  • Giant structure
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Comments

Mariah

These are good. Shame it's not all of the Chemistry Unit. Thanks =)

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