Periodic Table of the
Elements
Where did it come from?
• 1869 – Demitri Mendeleev
Russian chemist who discovered a pattern to the elements
• Wrote properties on cards
• Arranged cards according to properties and eventually tried increasing atomic mass
• A repeating pattern of similar properties then appeared
A Periodic Pattern
“periodic” = means happening at regular intervals
• Ex: Days of the Week
– Same order every 7 days
• Elemental properties repeat every seven elements
Mendeleev’s first try resulted with gaps in the pattern.
He predicted elements would fill in the gaps, but they had not yet been discovered.
Using the pattern he was able to predict their properties.
By 1886, all gaps were filled. His predictions were correct.
A Slight Tweak…
• A few elements did not fit the pattern in the table
• 1914 – Henry Moseley – British scientist who determined the number of protons (the
atomic number) in an atom of each element
• When elements were arranged by atomic number they all fit Mendeleev’s periodic pattern
Each Square Contains…
• Atomic Number
• Chemical Symbol
• Element’s Name
• Atomic Mass
6
C
Carbon
12.0
Period vs. Group
• Period
– Horizontal rows of elements
– Properties repeat in a pattern across the period
– Left Right: elements become less metallic
• All nonmetals are on the right!
• Group… aka Family
– Vertical column of elements
– Elements share chemical and physical properties
Break it Down
• Elements are classified in one of 3 categories depending on their properties.
• The number of electrons in the outer energy level of an atom helps determine in which category an element belongs.
• Metals -
• Nonmetals -
• Metalloids -
Metals
• Most elements
• Left of the zigzag line
• Few electrons in out level
• Most are solid at room temperature
– Exception: Mercury is a liquid
• Properties
– Shiny
– Malleable
– Electrically Conductive – Thermally Conductive
Nonmetals
• Right of zigzag line
• Most have complete sets of electrons in outer level
• Most are gases at room temperature
• Properties – (opposite of metals)
– Not shiny
– Not malleable (break if hit)
– Poor conductors of electricity and heat
Metalloids
• Border zigzag line
• 1/2 complete set of electrons in outer level
• Properties of metals and nonmetals
– Ex: Tellurium is shiny but is also brittle – Ex: Boron is hard like diamonds, but it is brittle.
It also is a could conductor of electric currents.
What are
the parts of an atom?
Protons
Neutrons
Electrons
INSIDE THE NUCLEUS
• Protons –
– Positive Charge
– Determine atomic number
• Neutrons –
– Neutral Charge
OUTSIDE THE NUCLEUS
• Electrons
– Negative Charge
– Located in energy levels
– Same as atomic number (atoms aren’t +/-)
• Protons and electrons cancel out!
Electrons are Often Shared in a Chemical Reaction to Make
Compounds
What goes in equals what comes out!
Which electrons are shared?
• VALENCE ELECTRONS: Electrons in the outermost energy level
How many valence electrons does an atom have?
Periodic Table
• Elements are grouped based on similar properties
• Elements in the same group (column) have the same number of valence electrons
• Group 1-2: Same as group number
• Group 3-12: No rule
• Groups 13-18: 10 fewer valence electrons than group number
– Exception: Helium has only 2 (not 8)
To bond or not to bond…
• Atoms with 8 electrons in outer level are not likely to form bonds because level is full
• Atoms with less than 8 are much more likely to form bonds because they want to fill the outer level
• Atoms with 1 electron with share with atoms that have only 7.
When is two enough?
• The first energy level in all atoms only holds two electrons.
• Some atoms have only one energy level.
• They are full with only two electrons not 8.
• Hydrogen, Lithium, and Helium
Lithium gives one away so it’s left with two.
Helpful Rules For Drawing Bohr Models
1. Period number tells the number of energy levels.
2. If an element is in Group 1-it will have 1 valence electron.
3. If an element is in Group 2-it will have 2 valence electrons.
4. If an element is in Group 13-it will have 3 valence electrons.
5. If an element is in Group 14- it will have 4 valence electrons.
6. If an element is in Group 15-it will have 5 valence electron.
7. If an element is in Group 16-it will have 6 valence electrons.
8. If an element is in Group 17-it will have 7 valence electrons.
9. If an element is in Group 18- it will have 8 valence electrons.
10. Atoms in elements in Groups 3-12 do not have a rule relating their valence electrons to their group number.
To Bond or Not to Bond
1. Valence electrons determine whether an atom forms bonds.
2. Atoms of Noble Gases do not usually form chemical bonds. All Noble Gases have 8 valence electrons (except helium).
3. An atom is considered to be full if the energy level contains 8 electrons.
4. Atom that has fewer than 8 valence
electrons is more likely to form bonds than an atom that has 8 valence electrons.
Group 1: Alkali Metals
• Li, Na, K, Rb, Cs, Fr
• Most reactive metals because atoms give up their only outer electron
easily
• 1 electron in outer level
• Only found in nature combined with other elements
• Properties: soft, color of silver, shiny, low density
• Pure metals often stored in oil-keeps from reacting with water or oxygen
Group 2: Alkaline-Earth Metals
• Be, Mg, Ca, Sr, Ba, Ra
• Not as reactive because they have 2 outer electrons that are not shared as easily as just one
• Properties: color of silver, higher
densities than alkali metals
Groups 3-12:
Transition Metals
• Less reactive than groups 1-2 because they do not share electrons easily
• Properties Vary Widely: Shiny, conductors of electric and thermal currents, higher densities and melting points than groups 1-2 (except
mercury)
– Most solid, but mercury is liquid – Most silver, but gold is… gold
– Some are not reactive (titanium used in medicine), but iron is very reactive (forms rust)
Lanthanides and Actinides
• Periods 6 and 7.
• Found at bottom of periodic table to keep table from being too wide.
• Transition metals
• Lanthanides: Shiny, reactive metals
• Actinides: Radioactive or unstable (change into atoms of another element) Elements after Plutonium do not occur in nature.
Group 13: Boron Group
• B = One metalloid
• Al, Ga, In, Tl = Four metals
• 3 electrons in outer level
• Very reactive
• Properties: solid at room temperature
• Aluminum is most common (earth’s crust)
Group 14: Carbon Group
• C = one nonmetal
• Si, Ge = two metalloids
• Sn, Pb = two metals
• Uuq = name to be determined
• 4 electrons in outer level
• Properties: solid at room temp and reactivity varies
• Si and Ge used to make computer chips
Group 15: Nitrogen Group
• N, P = two nonmetals
• As, Sb = two metalloids
• Bi = one metal
• 5 electrons in outer level
• Nitrogen = 80% of air you breath, fertilizers
• Properties: solid at room temp. (except
N) Reactivity varies among elements.
Group 16: Oxygen Group
• O, S, Se = Three nonmetals
• Te = One metalloid
• Po = One metal
• 6 electrons in outer level
• Properties: All but oxygen are solid at room temperature. Reactive.
• Oxygen makes up about 20% of the
air you breath!
Group 17: Halogens
• F, Cl, Br, I, At
• All nonmetals, very reactive
• Seven electrons in outer energy level so only need one to have a complete set (8)
• Combine with most metals to form salts
• Properties: Poor conductors of electric
current, violent reactions with alkali metals to form salts, never uncombined in nature
Group 18: Noble Gases
• He, Ne, Ar, Kr, Xe, Rn
• All nonmetals
• Very unreactive because they have 8 electrons in outer energy level (except helium which has 2)
• Properties: colorless, odorless gases at room temperature. Unreactive
Hydrogen
• Most abundant element in the universe
• Put above group 1 because it only has one electron in the outer energy level, but
properties are unlike any single group
• Properties: colorless, odorless gas at
room temperature; low density; explosive reactions with oxygen
