Unit 4:The Periodic TableHistory and Trends

Chapters 6 & 7Test - October 31, 2008

Periodic Table• A systematic arrangement of the elements by atomic number (protons)

• Similar properties fall into vertical columns

• Dmitri Mendeleev (1869) developed the first periodic table

• Arranged by increasingatomic mass

• Aligned properties invertical columns

•Some elements fell into the wrong column•Examples: Te & I ; Co & Ni

History of the Periodic Table

Mendeleev’s Periodic Table

• Henry Moseley (1913) rearranged the modern table by atomic number

• Used X-ray spectrometer to find the atomic numbers

History of the Periodic Table

Arrangement of thePeriodic Table

States on the Periodic Table

Red GasesBlack SolidsBlue Liquids

Types of ElementsMetals, Nonmetals, & Metalloids

Metals• Found on the left side of table• Have 1, 2 or 3 electrons in valence• Lose electrons to form positive ions (cations)

• Most are silver, shiny, solid, malleable, ductile & good heat/electrical conductors

Metals

Nonmetals• Found on the right side of table• Have 5, 6, or 7 electrons in valence• Gain electrons to form negative ions (anions)

• Brittle, dull, non-conductors, and exist in all three states (solids, liquids, gases)

Nonmetals

Metalloids• Elements found along the stairstep between metals and nonmetals, excluding Al

• B, Si, Ge, As, Sb, Te, Po• Properties are intermediate between metals & nonmetals

Metalloids

Oxidation Numbers

Metals+ ; lose valence electronsNonmetals- ; gain valence electronsMetalloidsoxidation numbers vary Transition elementsmultiple oxidation numbers

Number of electrons lost or gained when reacting to achieve full valence (ex: Na+ ; O2-)

Oxidation Numbers1+

2+ 3+ 1-2-3-4+/2+

0

Multiple oxidation numbers

Groups/Families• A group/family is a vertical column• They have similar properties("A" families only!!)

• Same # of valence electrons (roman numerals at the top)

"A" Group Families• Electron configuration ends in "s" or “p” sublevel• Referred to as the representative

elements

“A” Groups/Families

"B" Group Families• a.k.a. Transition Metals• Electron configuration ends in “d” sublevel

“B” Groups/Families

Inner-Transition Metals• 2 bottom rows• Electron configuration ends in “f” sublevels

• Really belong in rows 6 & 7 before transition metals

• Elements beyond #92 are man-made (too unstable to be found in nature)

Inner-Transition Metals

Group/Family NamesIA – Alkali Metals Most active metals Stored under oil

(water reactive) 1+ oxidation number Ex: Li, K

IA - Alkali Metals

Group/Family NamesIIA – Alkaline Earth Metals• Less reactive than IA• 2+ oxidation number• Ex: Mg, Ca, Sr

IIA - Alkaline Earth Metals

Group/Family NamesVIIA- Halogens • Most active nonmetals• 1- oxidation number• Ex: F, Cl

VIIA - Halogens

Group/Family NamesVIIIA – Noble Gases• Relatively inactive (inert)• Contain 8 valence electrons• All gases• Ex: Ne, Xe

VIIIA - Noble Gases

Hydrogen• Unique element, most abundant in the universe (75%)

• Nonmetal on the left side of the periodic table (found in metal column)

• Gas state• One valence electron

Hydrogen

Nitrogen As the chemically unreactive molecule N2,

makes up 78 percent by volume of Earth’s atmosphere. • Plants and animals can’t use nitrogen in this form.

• Lichens, soil bacteria, and bacteria in the root nodules of beans, clover and other similar plants convert nitrogen to ammonia and nitrate compounds.

• Lightning also converts atmospheric nitrogen to nitrogen monoxide (NO).

• Plants use these simple nitrogen compounds to make proteins and other complex nitrogen compounds that become part of the food chain.

Period/Series• Horizontal rows• Share the same number of energy levels

Periodic Table Trends• Atomic Radius• Electronegativity•Metal Activity•Nonmetal Activity

Atomic Radius• Half the distance between the

centers of two atoms that are just touching each other

• Influenced by two factors1. The number of energy levels in an atom2. The pull of the positively charged nucleus

on its electrons

The more energy levels, the ________ the atomic radius. (larger/smaller)

The more protons in the nucleus, the ________ the atomic radius. (larger/smaller)

Atomic Radius & IonsMetals lose electrons to form cations

Li Li+

F F-

Nonmetals gain electrons to form anions

Atomic radius decreases - energy level is lost or “shed”

Atomic radius increases - energy level expands because it is more “crowded” and electrons exert greater forces on each other

Ionic Radius

Atomic Radius - Trend• Atomic radius

increases as you move down a group

• Atomic radius decreases as you move from left to right in a period

Electronegativity

• How easily an atom attracts the valence electrons of another atom• Assigned number “rates” the electronegativity (from 0.7 to 4.0)

• Low electronegativity = does not want to attract valence electrons• High electronegativity = really wants to attract valence electrons

Electronegativity & Stability• Because of electronegativity…

• Stable atoms find it harder to bond with other atoms and have lower (re)activity• Example: noble gases

• Unstable atoms find it easier to bond with other atoms and have greater (re)activity• Example: alkali metals and halogens

Electronegativity - Trend• Electronegativity decreases as you move down a group

• Electronegativity increases as you move from left to right in a period

Metal Activity

• How easily metals lose e- to form cations• Since electronegativity is how easily atoms attract valence

electrons, the most active metals are the least electronegative (they want to lose e-)!

Trend•Increases as you move down a group•Decreases as you move from left to right in a period

*The most active metal is francium

decreasing metal activity

incr

easi

ng m

etal

act

ivity

Nonmetal Activity• How easily nonmetals gain e- to form anions• Since electronegativity is how easily atoms attract valence

electrons, the most active nonmetals are the most electronegative (they want to gain e-)!

Trend•Decreases as you move down a group•Increases as you move from left to right in a period

*The most active nonmetal is fluorine

increasing nonmetal activity

decr

easi

ng n

onm

etal

act

ivity

Question 1 Match each element in the left column with

the best matching description in the right column. Descriptions may be used more than once.

1. Strontium a. halogen2. Chromium b. alkaline earth metal3. Iodine c. representative element

d. transition element

Question 2 For each of the following pairs, predict

which atom is larger.A. Mg, SrB. Sr, SnC. Ge, SnD. Ge, BrE. Cr, W

Question 3 Compare the alkali and alkaline earth

metals in terms of position in the periodic table, number of valence electrons, and overall properties.

Question 4 Compare the metallic character of the

elements carbon, silicon, and lead. What do these elements have in common in terms of valance electrons and placement in the periodic table?