The Atom Year 9 Science 2012

Have you ever wondered?

Short Pre-Test: What do you know already? Draw what you think an atom looks like. Explain the term ion Describe roughly how many different types of atoms there are Define the difference between fission and fusion Explain some of the risks of nuclear radiation

Goals:

Vocab: Atom Atomic model Atomic number Atomic symbol Compound Electron configuration Electron shell Element Isotopes Mass number Molecule Neutral Neutron Nucleus Periodic table Proton Atom Atomic model Atomic number Atomic symbol Compound Crystal lattice electron

Atoms: Everything is made of atoms No one has ever seen an atom!

What we know about atom The are 119 known different atoms An only 95 of these are found on Earth

Atoms in elements and compounds

When elements stick together, they form clusters called COMPOUNDS or large grid-like structures called LATTICES

Elements: If a substance has only one type of atom, it is called an ELEMENT

Compounds: If a substance is made up of molecules or a crystal lattice with different types of atoms, then it is known as a compound

Lattices:

Inside Atoms: We now know that the atom is made from sub-atomic particles – protons, neutrons and electrons

Atomic Nuclei: The number of protons an atom has is called its ATOMIC NUMBER The number of protons + neutrons is called the atoms MASS NUMBER This is written:

Number of electrons in a neutral He atom: So, He is: Helium Number of protons = 2 protons Number of neutrons = 4 – 2 = 2 neutrons Number of electrons in a neutral He atom: 2 electrons

Activity Book: 1.1 Atomic symbols Page 1

Isotopes: Atoms of the same elements can have different numbers of neutrons Eg most Helium atoms have two protons and two neutrons, denotes by He-4 BUT: He-3 atoms also exist: These still have 2 protons (He) but only one neutron

Activity Book: 1.2 Isotopes Page 2-3

Focus on Electrons:

Electrons and the nucleus: If the number of electrons in an atom is EXACTLY equal to the number of protons, the atom is then NEUTRAL This is because the electrons have a negative charge and the protons have a positive charge

Electrons: Although each electron is 1800 times smaller than a proton, together the electrons form 'clouds' around the nucleus. The clouds can be 100 or even 1000 times wider than the nucleus. This means that if the nucleus was the size of a golf ball, the electrons would form clouds the size of a football stadium. It also means that most of an atom is empty space.

How do we now that the atom is mostly empty space?

Practical Activity: Experimenting like Rutherford

Ernst Rutherford: The New Zealand scientist Ernest Rutherford discovered that the nucleus only takes up a small fraction of the space inside an atom. In his famous experiment, Rutherford fired a beam of helium nuclei (alpha particles) at a thin sheet of gold foil.

To his surprise, most of the nuclei passed straight through the foil and only a small fraction were deflected back. Up until that point, most scientists had believed that atoms were completely solid. Rutherford realised that atoms are mostly empty space. However, they had a small, positively charged nucleus surrounded by a cloud of electrons.

Electron Shells: The electrons in an atom are attracted to the nucleus by the positive charge of the protons. However, the electrons never fall into the nucleus. This is because the electrons are trapped inside electron shells which surrounds the nucleus which surround the nucleus like the layers of an onion

Once the 1st electron shell is full, electrons start to fill the 2nd electron shell, which can hold up to 8 electrons. The 3rd electron shell holds up to 18 electrons. The 4th electron shell can hold 32 electrons.

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Electron Shells: Many of the electron shells in an atom are empty. The biggest known element at present has 118 electrons in 6 shells. The 1st electron shell is the innermost shell. It is the smallest electron shell and can only contain 2 electrons.

Electronic Configuration: The number of electrons in each shell of an atom is known as its electron configuration For example, carbon has 6 protons and therefore 6 electrons. The first 2 electrons fill the 1st electron shell, and the remaining 4 electrons go into the 2nd electron shell. Therefore the electron configuration for carbon is 2,4

Activity Book: 1.4 Electronic Configuration of Ions: Page 6-7

The Atomic Model:

Activity Book: 1.3 Model Scientists Page 4-5

Revision Questions: How many protons, neutrons and electrons are in a potassium atom? ( 2919K ) Describe the structure of a potassium atom Potassium forms a metal lattice. What does this mean? Talcum powder is a compound made from powdered magnesium oxide. What is a compound? The compound magnesium oxide does not contain molecules. What are molecules? Will the properties of magnesium oxide be an average of the properties of magnesium and oxygen?