Elements andAtoms

Chapter 9(Chemistry)

How many different substances are there?

There are millions of different substances! What are they all made of?

How many different substances

can you think of?

All substances are made of atoms

ATOM = tiny particle that all substances are made up of

Many substances are made up of different types of atoms.

What is an element?All substances are made of very tiny particles called atoms.

copper

carbon

ELEMENT = substance that is made up of just one type of atom.

helium

Discovery of elements- Before 1669 the following elements have already been discovered:- Carbon- Sulphur- Iron- Copper- Arsenic- Silver- Tin- Antimony- Gold- Mercury and- Lead

An element is a substance made up of only one type of atom

Atoms in elements

Copper is an element made up of copper atoms only.

Carbon is an element made up of Carbon atoms only.

Helium is an element made up of helium atoms only.

The properties of elements

- Each element has its own properties. Example:- Bromine and mercury are the only 2 elements that are liquid at room

temperature.

- Eleven elements are gas at room temperature.- Sodium is a silvery white metal with a melting point of 98⁰C and a boiling

point of 884⁰C

- Chlorine is a yellowish green gas with a melting point of -101⁰C and a boiling point of -34 ⁰C

- Most substances are made of 2 or more elements joined together (compounds).

- When elements form compounds they no longer show their own special properties.

- The compound now has its own special property. Example:Sodium + Chlorine Sodium chloride- Sodium chloride is a white solid with a melting point of 801⁰C and a boiling

point of 1420⁰C and easily forms crystals

- Compounds of some elements are used in fireworks due to the colour they produce when they are heated.

Chemical symbols

- The first chemists where called alchemists.- 2 of their main activities where investigating materials in an attempt to:(a) make gold(b) make a medicine which would extend the human life span.

- The alchemists wrote down details of substances using symbols to save time.- They used mysterious symbols to keep their work a secret.- Later on when the science of chemistry began properly scientists decided

that any substance used for an investigation or produced from it should be clearly identified by one name only.

- Each element is identified by the first letter of its name.- If two or more elements begin with the same letter another letter of the

name is used. Example: Hydrogen (H) and Helium (He)- Some of the symbols are made from their old names, Example:(a) Iron -------- old name Ferrum --------- Fe(b) Silver ------ old name Argentum ------ Ag(c) Sodium --- old name Natrium -------- Na(d) Potassium - old name Kalium --------- K

- In 1813 Jons Jakob Berzelius introduced the symbols we still use today to represent the elements.

- After a large number of elements had been identified, scientist began arranging them into order based on their properties, such as mass.

- A table called the periodic table was produced.- The atoms of the elements increase in mass as you progress from left to right

and downwards in the periodic table. (1 atom of H has less mass than 1 atom of Na)

The first 20 elements in the periodic table

- Each element has:(a) Atomic number: Tells how many protons the element has.(b) Mass number (atomic mass): Tells how many protons and neutrons each

atom in the element has in total.

- N.B.- Protons -------------- +ive charge- Electrons ------------ -ive chargeBut, the atom has no overall charge (no. of protons = no. of electrons)

Identify:a) The number of protons?

b) The number of electrons?

c) The number of neutrons?

d) The atomic mass (Mass number)?

- The electrons are arranged in electron shells or orbits around the nucleus.

- This is the electronic structure.- The first shell has only room for two electrons.- The second and the third shells each have room for up

to eight electrons.- The electron arrangement of the atom is often written

as numbers.- Example the electron arrangement of carbon is 2, 4

(this means 2 electrons in the first shell and 4 in the 2nd shell).

Arranging the electrons

Carbon atom

The first 2 elements of the periodic table

(TO BE MEMORISED)