Atomic structure Gr.7 2018

Atomic structure Gr.7

1. AtomS The building unit of the universe!

2. Democritus 460-370 BC A Greek philosopher The first to suggest the idea of atoms. ( atomos in Greek= indivisible) Unlike other philosophers of his time that believed that all matter could be reduced to a combination of four elements: earth, water air and fire.

3. 19 th century Elements are made up of atoms . An atom is the smallest part of an element that can exist. Atoms of different elements have different structure, which is the reason why the different elements have different properties. Experiments by John Dalton and other scientists helped us to understand more the nature and structure of atoms.

4. Atomic structure

5. Atoms are made of smaller particles found in the center – nucleus - that contains protons and neutrons, and other smaller particles called electrons moving around the nucleus in circles . A Proton is positively charged particles that have a relative mass of 1 . Neutrons are neutral (have no charge) have mass of 1. Atomic mass of an element is the total mass of protons and neutrons . Electrons are negatively charged particles that move around the nucleus constantly. Around 1850 electrons together will have the same mass of a proton, we usually neglect the mass of electrons when measuring the atomic mass.

6. Information found in the periodic table Atomic number Number of protons in the atom Chemical symbol Consists of one or two letters first is capital. Element name Atomic mass Mass of nucleus (protons + neutrons)

7. Atomic mass & atomic number Atomic number = protons Atomic mass = protons + neutrons Open p. 154 and use the periodic table, to find the number of protons, electrons and neutrons in these elements: Be, Cr, Al, Sc , Se, He, F, O, C, Au, Na, Ca, Ne, Si

8. Can you tell which element this atom is?

9. Electronic configuration When electrons move around the nucleus they do so at specific distances from the nucleus, we call them orbits or energy levels. As the electrons fill up the energy levels they begin with the closest to the nucleus. You need to remember that the first energy level takes 2 electrons, the second takes 8 & the third takes 8 . For example, the electronic configuration of sodium is 2, 8, 1.