1. Atomic Structure and the Periodic Table Chapter 2-1

2. Chemical symbols Abbreviated way to write the name of an element Always starts with a capital letter If double letters – first is capitalized second is lower case Cl Ar Ne

3. atom Smallest part of matter Basic building block of matter Parts of an atom – Nucleus – center – – protons - + charge – neutrons - neutral charge size: mass p = mass n

4. Electron cloud – Surrounds the nucleus – Contains electrons – Electrons have a negative charge – Size: mass e = 1/2000 of m p – mass so tiny that it isn’t even considered in the mass of an atom – Moves around the nucleus at such speeds that they cannot be seen. – Cloud like appearance

5. – Neutral atom – the number of positive charges equal the number of negative charges – All elements on periodic table are stable atoms.

6. Atomic number Number of protons in an atom Every atom of the same element has the same atomic number Identity number of an element

7. Danish scientist Neils Bohr 1913 Developed the first model of what the atom looks like

8. Bohr diagram Central nucleus Electrons moving around it in well defined paths or orbits.

9. Electron clouds Electrons moving so fast that they cannot be seen Electrons move within a certain region NOT on orbits

10. Energy Levels and Electrons Electrons are at varying distances from nucleus – e near nucleus – low energy – e farther from nucleus – high energy

11. Energy levels – Each holds a different amount of electrons – There is a maximum number of electrons each can hold

12. 1 st 2 e 2 nd 8 e 3 rd 18 e 4 th 32 e

13. Mass number – Number of protons + neutrons in nucleus

14. Number of Neutrons Mass number - # p = #n

15. Isotopes Atoms of the same element that have a different number of neutrons Average atomic mass – average mass of an element and its isotopes Written H-1 H-2 H-3 element – mass #

19. Isotopes of hydrogen H-1 protium H-2 deuterium H-3 tritium

20. Importance of Isotopes Used in: Medical field – radioactive to detect cancers, thyroid disorders Dating – to date age of rocks or artifacts Radioactive power plants