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

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

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)

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!

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

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)

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

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

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…

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?

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

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

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