Atoms, elements and the Periodic Table.

Print pages 9-13 2 page handouts

What is an Atom.• Atoms are the basic building blocks of ordinary matter. Atoms can

join together to form molecules, which form most of the objects around you.

• Atoms are composed of particles called protons, electrons and neutrons. Protons carry a positive electrical charge, electrons carry a negative electrical charge and neutrons carry no electrical charge at all. The protons and neutrons cluster together in the central part of the atom, called the nucleus, and the electrons orbit the nucleus. A particular atom will have the same number of protons and electrons and most atoms have at least as many neutrons as protons.

proton

Neutron

Electron

A proton is a part of an atom. The other parts of an atom are the neutron, and electrons. It's an electrically charged particle. It is positive. It is located within the nucleus of the atom, which is about one ten thousandth of the diameter of the atom itself but contains virtually all of the atom's mass. The number of protons in the nucleus determine the element.

A neutron is a subatomic particle; it is one of the building blocks of the atom. As such, it is found in the nucleus of an atom. It has no electric charge. It has a half ;life of 886 seconds.

An electron is a subatomic particle that has a negative charge. An electron has like a weird orbit around the proton/neutron but doesn`t fully orbit them it pops up here and there.

Atoms and Elements.The word ATOM was first used in the fifth century BC by a Greek thinker called Leucippus. He Thought everything was made of tiny particles that could not be divided. However, nobody believed him. John Dalton put forward his theory about atomic theory in 1807.

The structure of a helium atom.

Each element has its own symbol. This is a shorthand way of writing down the elements, and is the same whatever language spoken by the scientists. The symbol have one or two letters. For example Oxygen is O and sodium is Na. The first letter is a capital letter.

The periodic

table

Name of element

Symbol for the element

(Atomic mass)Protons and neutrons added together

(Atomic number)The number of protonsMust contain 2 electrons

The meaning of the symbols

All elements arranged into increasing atomic number.

The vertical columns are called groups. They are called groups becauseThey are similar to each other. For example group 1 are all very re-active metalsAnd group 2-3 they contain a lot of metals.

Atomic StructureAtoms are made up of three different kinds of particles called Neutrons, protons and electrons.The masses of these particles are really tiny. We say protons and neutrons have a mass of 1. Electrons are smaller they do have a mass but that is so small we can ignore it. We say that Electrons have a negligible mass. Protons and electrons have electric charges. Protons have (+) Charge, and electrons have a (-) charge. Atoms always have the same amount of protons and Electrons so the charges cancel each other out. Atoms have no overall electrical charge. Each Atom in an element has the same number of protons. A different element will have a different Number of protons in it`s atom. The number of protons in an atom is called it`s atomic number.

A hydrogen nucleus. Hydrogen atoms always Have just one proton in The nucleus. The atomic Number of hydrogen is 1

A carob nucleus. CarbonAtoms always have six protons.The atomic number of carbon is 6

An oxygen atom nucleus Oxygen atoms always have Eight protons. The atomic number Of oxygen is 8

The mass of an atom depends on the number of protons and neutrons. The total number of Protons and neutrons is an atom is called its mass number. Carbon has six protons and six Neutrons so it has a mass number of 12. sometimes atoms of an element have different numbersOf neutrons. Isotopes are atoms of the same element that have different numbers of neutrons.Most elements have different isotopes.

Electronic structureSome elements are very reactive, and some hardly react at all. Elements behave differently Because of the way their electrons are arranged. Electrons have a negative charge, and protonsHave a positive charge. An atom normally has the same number of protons and electrons, so itHas no overall charge.

Hydrogen has just one Proton.One electron moves around it

Helium has two protons andTwo neutrons in it`s nucleus.It has two electrons movingAround the nucleus.

Lithium has three protons and Three electrons. Two of the Electrons are close to the nucleus,And the third one is further away.These different locations for Electrons are called energy levels/Shells. The inner shell can only holdTwo electrons they the outer shellsHold up to 8

The periodic table.

12MG

2,8,2

ATOMIC NUMBER (NUMBER OF PROTONS)

SYMBOL (MAGNESIUM)ELECTRONIC STRUCTURE

The elements are arranged in the periodic table in order of the atomic number. The position of An element in the periodic table can also tell us something about how the element reacts. OnlyThe electrons in the outer shell of an atom will take part in chemical reaction. They also form Similar compounds. Some properties change as you go down a group. For instance, elements atThe top of a group may have lower melting and boiling points than ones at the bottom. The Elements can be split into metals and non-metals.

12MG

2,8,2

nucleus

This diagram shows the inner shellHas two electrons in because the firstNumber of the electronic structure is 2Then the second shell has 8 electrons inBecause the second number is 8 andThe third shell has 2 electrons inBecause the last number is two onThe electronic structure.

Looking for patternsOne way scientists learn more about the world is to look for patterns, and then try to explainWhy these patterns exist. Johan Döbereiner was one of the first scientists to look for patternsOf properties in the elements. He noticed that chlorine, bromine and iodine had similar Properties. In 1864 John Newlands decided to put all the elements in order of masses of atoms.When he did this he found that the elements could be divided into groups, with every 8th Element having similar properties. He called this the law of Octaves.

1 H F Cl Co&Ni Br Pd I Pt&Ir

2 Li Na K Cu Rb Ag Cs TI

3 G Mg Ca Zn Sr Bd Ba&V Pb

4 Bo Al Cr Y Ce&La U Ta Th

5 C Si Ti In Zr Sn W Hg

6 N P Mn As Di&Mo Sb Nb Bi

7 O S Fe Se Ro&Ru Te Au Os

Most scientists ignore Newlands theory because his law did not work for all the elements. A Russian scientist Dmitri Mendeleev arranged elements like their modernorder. He around them

In order of mass number but he also looked at their properties. If the order of mass numbers put Elements in the wrong place for their properties, he ignored the masses.

Looking for patterns

He also left gaps in the table where there was no elements that fitted the pattern. He predictedThe mass numbers and other properties of these missing elements. In 1874 a French scientist Called Paul-Emile Lecoq discovered Gallium one of the missing elements and found that it hadProperties very similar to the properties predicted by Mendeleev. It was not until the structure of The atom was discovered in 1910 that scientists realised that Mendeleev`s order for the elementsDepended on the atomic number (the number of protons in the nucleus) rather than mass Number.