1. Chapter 4 Atoms & Elements
DE Chemistry – King William High School
Chapter 4 Atoms & Elements

2. 1 – Elements & Symbols Elements are pure substances
Symbols – you know these from last year 

3. 2 – Periodic Table Dmitri Mendeleev (1872) Periods – horizontal rows
Group (family) – vertical column (tend to have the same reactivity)
Representative (or main-block) elements = groups 1-2, 13-18)
Transition elements (“junk in the middle”)
Lanthanides & actinides (inner transition metals)

4. Groups… Alkali metals (group 1) – the most reactive metals
Alkaline earth (group 2) – not as reactive as alkali
Halogens (group 17) – most reactive nonmetals
Noble gases (group 18) – inert…don’t react!

5. The staircase… Separates the metals from the nonmetals
Metals to the left (ductile, malleable, good conductors of heat)
Nonmetals to the right (poor conductors, low MP, low density)
Metalloids on the staircase (EXCEPT Al Aluminum is a metal!)
Metalloids are semiconductors because they can act as conductors and insulators

6. 5 – The Atom
An atom is the smallest part of an element that retains the characteristics of that element
1808 – John Dalton’s Atomic Theory (see page 105 to refresh your memory)
J. J. Thompson (1897) – plum pudding model
Rutherford – Gold foil experiment (discovered the nucleus)

7. More on the atom… Subatomic particles – proton, electron & neutron
Protons & neutrons contain most of the mass in the nucleus
Electrons are very small and zoom around outside of the nucleus

8. 4 – Atomic # & Mass # Atomic number = number of protons
Atomic number = number of electrons (in a neutral atom)
Mass number = protons + neutrons

9. 5 – Isotopes & Atomic mass
Isotopes – same element with different number of neutrons
Carbon-12 & carbon-13
Average atomic mass = decimal # on periodic table
Formula for calculating…

10. EXAMPLE…
A new element Fulksium has been discovered at KWHS. It has two isotopes: Fu-363 has a relative abundance of 37% and Fu-364 has a relative abundance of 63%. What is its average atomic mass?

11. 6 – Electron Energy Levels
Energy level = the specific energy of an electron
The higher the number then the higher the energy
The higher the energy then the further away form the nucleus

12. 7 – Trends (Periodicity)
Valance electrons
Atomic size or radius (Fr)
Ionization energy (energy needed to remove an electron)  F
Metallic character (loses valence electrons easily)  Fr

13. Lewis Dot…just the basics
Only for elements…no compounds. As Cl Ne