The Atom By Miss Buicke

What we must know from the syllabus: OC39 Describe the structure of the atom, state the location, relative charge, and atomic mass of the sub-atomic particles, and define atomic number and isotope. OC40 Draw the Bohr structure of the first 20 elements.

An atom: The smallest part of an element which still has the properties of that element. The word atom comes from a Greek word meaning something which cannot be split.

Inside the atom: The atom consists of three sub-atomic particles  Protons  Neutrons  Electrons

Properties of each of the sub-atomic particles :

All the particles are extremely small. Electrons are so small it would take almost 2000 of them to have the same mass as a single proton or neutron. As a result the mass of an electron is rounded off to zero. Protons and neutrons are of similar mass.

Atomic and Mass numbers The atomic number of an element: The number of protons in an atom of that element. The atomic number of an element: The number of protons in an atom of that element. The mass number: The total number of protons and neutrons in an atom of that element. The mass number: The total number of protons and neutrons in an atom of that element.

Atoms of different elements differ from each other by the number of protons, neutrons and electrons they have. Each element in the periodic table has a number written above and below its symbol. The smaller number is called the atomic number. This tells us how many protons every atom of that element has. The number of protons in an atom is always equal to the number of electrons. Because of this atoms are neutral. The charge of the proton cancels out the charge on the electron. Atoms of different elements differ from each other by the number of protons, neutrons and electrons they have. Each element in the periodic table has a number written above and below its symbol. The smaller number is called the atomic number. This tells us how many protons every atom of that element has. The number of protons in an atom is always equal to the number of electrons. Because of this atoms are neutral. The charge of the proton cancels out the charge on the electron.

Examples :

Atomic number: 6 protons Mass number: Number of protons and neutrons 12-6 =6 neutrons 6 protons + 6 neutrons= 12 Atomic number: 6 protons Mass number: Number of protons and neutrons 12-6 =6 neutrons 6 protons + 6 neutrons= 12

Atomic number: Number of protons = 3 Atomic number: Number of protons = 3 Mass number: Number of protons and neutrons. Number of neutrons: 7-3 =4 Number of protons 3 + number of neutrons 4. Mass number= = 7 Mass number: Number of protons and neutrons. Number of neutrons: 7-3 =4 Number of protons 3 + number of neutrons 4. Mass number= = 7

How electrons are arranged: Electrons whizz around the nucleus in energy levels called shells or orbitals. The first shell can hold two electrons. The second and third shell can hold 8 electrons each Electrons fill up the shells one by one, starting with the first shell. When a shell is full, they start a new one.

Two electrons can only go in the first shell

The atomic structure (The Bohr Model) We must be able to draw the atomic structures of the first twenty elements in the periodic table. Niels Bohr was the first person to put forward the idea of electron shells containing electrons orbiting the nucleus. Niels Bohr was the first person to put forward the idea of electron shells containing electrons orbiting the nucleus. The way these electrons are arranged in each shell is called the electronic configuration. The way these electrons are arranged in each shell is called the electronic configuration.

Examples using the Bohr model

12 electrons18 electrons ELECTRONIC CONFIGURATION: (2,8,2) ELECTRONIC CONFIGURATION: (2,8,8)

Isotopes: Atoms of the same element which have different numbers of neutrons Isotopes: Atoms of the same element which have different numbers of neutrons A popular pair of isotopes are carbon-12 and carbon-13 which are used in carbon dating. Both of these atoms have an atomic number of 6 which means they are both carbon. However they have different mass numbers and as a result they have different numbers of neutrons in their nucleus. A popular pair of isotopes are carbon-12 and carbon-13 which are used in carbon dating. Both of these atoms have an atomic number of 6 which means they are both carbon. However they have different mass numbers and as a result they have different numbers of neutrons in their nucleus.