Chemistry Lessons (Atomic Structure) - Knowledge Structure’and’Configurations’ !...

Kevin Small www.cxctutor.org or www.cxctutor.com

Atomic Structure

Quick Review: We have talked about the 3 states of matter; their transformations and characteristics.


We discussed the nature of matter.

Matter is anything that has mass and occupies space. All matter is made of up particles which can exist in the 3 states mentioned above.

But what evidence do we have that matter exists? The following terms give us evidence of matter:

1. Crystals have regular shape – For example look at a single grain of common salt. All crystals of the same substance have straight edges, flat surfaces and the same shape. This suggests that particles of crystals are arranged in regular repeated rows.

3. Dilution – Think of when you mix sweet and dandy mauby syrup with water; you can add a lot of water and the solution will still retain a colour. A better example would be to that given in no. 2 above when a small crystal of potassium manganate (VII) is


dissolved in a beaker of water. The fact that the solution retains a colour although diluted a 1000x times suggests that the crystal is made up of many tiny particles.

4. Brownian Motion – Named after the botanist Robert Brown in 1827, as he observed pollen dust in water. This term refers to the haphazard movement of small particles as

they are being collided by even smaller particles such as air or water molecules.

We started to distinguish between compounds and mixtures.

• A compound is a substance composed of two or more different types of elements bonded together chemically in fixed proportions and in such a way that their properties are changed. They are not easily separated and new chemical properties have been formed.

• A mixture consists of two or more substances (which can be elements or compounds etc.) which are brought in close contact with each other in varying proportions but they


don’t react. Mixtures are easily separated by physical means (i.e. a fruit\salad mixture). There is no change in chemical properties. Look up separation techniques.

Atomic Structure and Configurations

An element is a pure tangible substance that cannot be split into anything simpler by any chemical process. We split elements into 2 categories: metal and non-‐metal.

However they are made up of molecules and molecules can be split into individual atoms.

A molecule is the smallest uncharged part of an element or compound which can exist on its own. E.g. Oxygen gas can only exist as the molecule O2 and Water is the molecule H2O.

An atom is the smallest characteristic part of an element that can take part in chemical reactions.

So in order of size:

Sub-‐atomic Particles:-‐

Atoms consist of three types of particles:-‐

• Protons

Ma[er

Elements

Molecules/Compounds

Atoms


• Neutrons

• Electrons

Table showing the relative charges and masses of the 3 sub-‐atomic particles along with their founders and the time period in which they were discovered:-‐

Date

Person who made the discovery

Particle developed

Relative mass of particle

Relative charge of particle

1897 J.J Thomson Electron 1/1840 -1

1919 E. Rutherford Proton 1 +1

1932 J. Chadwick Neutron 1 0

The structure of a typical atom:-‐

Atoms usually have equal numbers of protons and electrons inside of them. The charges on the protons (+1) and electrons (-‐1) are equal, but opposite, so they cancel out and the atom is said to be electrically neutral or stable.

Nuclear symbols:-‐

Atomic number: -‐ this is the number of protons in the nucleus of an atom; the symbol is: Z.

Neutron number: -‐ the number of neutrons in the atom is symbolised by N.


Mass number: -‐ the total number of protons and neutrons within the nucleus of an atom; the symbol is: A.

Hence the equation: -‐

A = Z + N

The atomic number and mass number of one atom of an element can be included with the symbol of the element:

Example: -‐

2311Na represents 1 atom of the element sodium:

Mass number = 23

Atomic number = 11

No# of protons = 11

No# of electrons = 11

No# of neutrons = (23 – 11) = 12

Chemistry Lessons (Atomic Structure) - Knowledge Structure’and’Configurations’ !...

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