Chapter 10
Atomic Structure & Periodic Table
Atom: smallest part of element
-name comes from “atomos” which means “not to be cut”
Element: A substance made of only 1 type of ATOM that can’t be broken down
-atoms of elements are the building blocks of all matter- on all planets!
Molecule: made of 2 or more ATOMS chemically combined – smallest part of a compound
Compound: A substance made of 2 or more ELEMENTS chemically combined
-formed when elements bond together
Atomic Models (model: a REPRESENTATION of something too big/small to see or hard to understand)
Democritus (4 Century BC)
-Greek philosopher suggested the universe was made of indivisible units
-named them “atoms” from the Greek word “atomos” which means ‘not to be cut’)
-thought the movements of atoms caused the changes in matter
-didn’t have evidence to back up his ideas
John Dalton (early 1800’s)
-thought atoms were solid balls & each element had their own kind
JJ Thomson (late 1800’s) – “plum pudding” model or “choc. Chip cookie” model
-thought atoms were a ball of positive charge with negatives spread through out
Rutherford & Bohr (early 1900’s) “Solar System” model
-thought atoms had a dense positive center with electrons in certain orbits
Electron Cloud Model (today)
-nucleus is positive
-“Cloud” is a region where electrons move, but not in orbits
2 Kinds of Bonds
Ionic Bond: Bond formed when electrons are gained or lost between elements creating opposite charges
Ion: a charged particle (has a + or a – charge), created when an element gains or loses eCation: + ion (has lost electrons and has more protons)
Anion: - ion (has gained electrons and has more electrons)
Covalent Bond: Bond formed when electrons are shared between elements
3 Parts of An Atom
Proton (p+)
- In the nucleus & has a positive charge
- amount NEVER changes- identifies the element
- Same amount, but opposite charge of the electron
- Same mass as neutron
- Atomic # = the whole number on the periodic table tells how many protons there are
Electron (e-)
- Outside the nucleus in the “electron cloud” and has a negative charge
- 1800x less mass than proton & neutron
- Electron cloud – region outside nucleus where electrons move, but NOT in orbits
o
o
o
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Made mostly of empty space
Electrons are in pairs
Levels that are “full” or “half full” or have 8 are stable- don’t combine
Has different energy levels with certain amount of electrons (2 n2 where n = the number of level)
 1st level = 2 electrons
2nd level = 8 electrons
rd
3 level = 18 electrons
4th level = 32 electrons
Neutron (n0)
- In the nucleus and has no charge
- Has same mass as proton
- The amount can vary from atom to atom in the same element
Quarks
- Smaller particles that make up protons & neutrons
- 6 types of quarks- It takes 3 quarks to make a proton or neutron
- Were studied by the Tevatron machine
Atomic Mass
- The mass of atom comes from protons & neutrons
- Mass # = Decimal number on the periodic table – it tells how many protons & neutrons it has
- # Neutrons = mass # - atomic #
Isotopes
-isotopes – atoms of the same element with different numbers of neutrons
-average atomic mass = the average of all the isotopes of that element
2 ways to show isotopes
- name is followed by the mass # like Carbon -12
12C
= 12 = mass #, 6 = atomic #
6
3 Classifications of Elements
Pure: Elements that are pure (not combined with anything) in their free state
Natural: Elements that exist in nature, but usually combined with another
-Hydrogen is the most common in universe
Artificial: Elements that are made in a lab
-don’t last long, break down
3 Types of Elements And Their Properties
Metals
Shiny
3 or less valence electrons
Good conductors of energy
Lose electrons when bonding
Malleable (hammered flat)
Ductile (rolled into wire)
Non-Metals
Dull
5 or more valence electrons
Poor conductors of energy
Gain electrons when bonding
Brittle Solids or gases
Metalloids
Have properties of metals & non metals
Depends on the element
Along the stair step line
The Periodic Table
-called ‘periodic’ because properties repeat at intervals
-Dmitri Meendeleev 1st to develop the periodic table- classified elements & arranged according to mass
-Henry Mosely arranged it by properties & atomic numbers
18 Vertical Columns
Horizontal Rows
-called ‘groups’ or ‘families’(have similar properties)
- called ‘periods’ (elements have different traits
Group # on top tells you the valence electrons
(valence electrons – e- in outer shell)
-Period number on the left tells the number
of energy levels that element has
-Group 1: Alkali Metals
- very reactive (easily loses 1 e-)
- has 1 valence (outer) electron
-Group 2: Alkaline Earth Metals
- also reactive (easily loses 2 e-)
-has 2 valence (outer) electrons
-Groups 3-12: Transition Metals
- usually have 1 or 2 valence (outer) electrons
-Groups 13-16:
- takes the name of the 1st element (oxygen family, nitrogen family etc.)
- # of valence equals 2nd number in group #
- Group 13 = 3 valence, Group 14 = 4 valence, Group 15 = 5 valence, Group 16 = 6
-Group 17: Halogens
- these are the “salt formers”
- very reactive (easily gains 1 e-)
-has 7 valence e-Group 18: Noble Gases (previously the “inert gases” from ‘iners’ meaning lazy)
- has 8 valence electrons = NOT reactive
-very stable- don’t gain or lose e-, don’t bond with other elements