PERIODIC TABLEChapter 5

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ORGANIZING THE ELEMENTS

Section 1

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LET’S REVIEW!• Chemical properties

• Any property that can only be tested by changing the chemical make-up of the substance.

• Physical properties

• Any property that can be tested without changing the chemical make-up of the substance

• Atomic mass

• Mass of protons and neutrons

• Atomic number

• Unique to each element, same as number of protons

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DMITRI MENDELEEV

• 1870, there were 63 elements known to man

• He organized them in order of their atomic mass, and saw a pattern from their properties.

•Was working on this while Thomson and Rutherford were still “exploring” the atom

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DMITRI MENDELEEV

• Arranged his table with repeating properties in columns, starting a new row each time the chemical properties repeated

• Left blank spaces in his table, concluding that these spaces were elements that hadn’t been discovered yet.

• Based on the patterns and the other elements around the blank space, he predicted the properties of those elements

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AN EXAMPLEWhat he called ekasilicon – it was discovered a few years

later

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Prediction

Atomic Mass 72 amu

Density 5.5 g/mL

Appearance dark gray metal

Melting Point high melting point

Germanium

72.6 amu

5.3 g/mL

gray metal

937o C

MENDELEEV’S TABLE

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DMITRI MENDELEEV

• Some problems arose…

• A few elements appeared to be slightly out of place

• Mendeleev put them in the right place and said their atomic masses were incorrectly measured

• However, he was actually arranging them by the wrong number

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HENRY MOSELEY

• ~1910: Discovered atomic number

• He rearranged the periodic table by this number and it fell into perfect order

• Mendeleev’s table worked because as the number of protons increase, the atomic mass should increase, however if there are fewer neutrons it could decrease

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PERIODIC LAW

• Periodic Law: physical and chemical properties of the elements are periodic functions of their atomic numbers

• In other words, when the elements are arranged by their atomic numbers, you should see chemical and physical properties repeating themselves

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ROWS

• Left to right – called periods

• Elements in the same periods show a pattern

• As you move left to right, conductivity and reactivity change, and elements become less metallic

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COLUMNS

• Top to bottom – called groups

• Elements in a group have similar chemical properties

• The elements in the same group (column) have the same number of valence electrons

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EXPLORING THE PERIODIC TABLE

Section 2

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REMEMBER

•The periodic table is organized by atomic number

•For a neutral atom, the number of protons equals the number of electrons 14

VALENCE ELECTRONS

• The trends found in a periodic table are a result of electron arrangement, specifically, the number of valence electrons

• Valence Electron: electrons in the outermost shell

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VALENCE ELECTRONS

• The group number of an element will tell you the number of valence electrons it has• Group 1 elements: 1 valence electron

• Group 2 elements: 2 valence e- ’s

• Skip the middle

• Group 13 elements: 3 valence e- ’s

• Groups 14-18 elements: 4, 5, 6, 7, and 8 valence e-

’s respectively. 16

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WHY DO WE CARE ABOUT ELECTRONS?

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ION

• A neutral, stable atom will have equal protons and electrons

•When an atom gains/loses electron(s), the atom is no longer neutral and has a charge

• It becomes an ion

• Ion: a charged atom19

ION• Ionization: When atoms EITHER gain or lose

electrons

• All atoms want to have 8 valence electrons in the outer shell – this would make their outer shell full

• Elements that are really close to having 8 electrons, desperately want to get there, and tend to be the most reactive.

• Elements that are already “full” are considered inert, they don’t react because they don’t need to gain or lose electrons

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LET’S RECALL

• Protons = positive charge

• Electrons = negative charge

• p+ # CANNOT change, but e- # can

• So…

• If an atom GAINED electrons, would they be more positive, or more negative?

• If they LOST electrons?

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CATION

• Remember…group 1 elements have 1 electron in their outer shell

• So…group 1 elements like to give up their single electron

• This would make it more POSITIVE

• We call this a cation

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ANION

• Remember…elements in group 17 have 7 electrons in its valence shell (it would like 8)

• So…it will accept an electron from a “donor”

• This would make it more NEGATIVE

• We call this an anion23

LET’S PRACTICE

• Group 16 Give Up? or Gain?

• Group 13 Give Up? or Gain?

• Group 15 Give Up? or Gain?

• Group 2 Give Up? or Gain?

• Group 1 Give Up? or Gain?

• Group 17 Give Up? or Gain?24

CHARGES

•How do we know if an atom is an ion?

•We show it with an exponent

•Cations have a +, and anions have a –• If an atom has gained 3 electrons• It is more negative = Al3-

• If an atom has lost 3 electrons• It is more positive = Al3+

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THE PERIODIC TABLE

• It is divided into three major categories

• Metals

• Nonmetals

• Metalloids (semiconductors)

• These categories are based on general properties and are further broken down into families

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• Metals are left of the “staircase”

• Nonmetals are to the right

• Metalloids share properties of both

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METALS

• Most elements are metals

• Like to give up their valence electrons

• Physical properties

• high luster (shiny), conductive (heat and electricity), malleable (bendable), ductile (stretchable), high density, high melting point

• All except Hg are solids at room temperature

• Chemical properties

• Most will react with oxygen 28

NONMETALS

• Like to gain electrons

• Physical properties

• dull, don’t conduct, brittle, low density, low melting points

• Like ashes (mainly carbon)

• Can be solid, liquid or gas at room temperature depending on the element. 29

METALLOIDS (SEMICONDUCTORS)

• Share properties of both metals and nonmetals• Can be shiny or dull, conduct ok, ductile and

malleable or brittle• These elements have become really

important because of the computer revolution• Computer chips are made out of

semiconductors (normally Si)• By position Al is a metalloid, but its

properties make it a light metal

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FAMILIES OF ELEMENTS

Section 3

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FAMILIES• Families of elements have

similar properties

• Each family also has the same number of valence electrons

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METALS

Alkali Metals, Alkaline-Earth Metals, Transition Metals

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ALKALI METALS

• Group 1 (excluding H)

• 1 valence e-

• Very reactive, especially with water

• Soft, shiny white metals (can be cut with a knife!)

• Low density (Li, Na, and K float in water)

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HYDROGEN

• Hydrogen is in group 1 but is not an alkali metal, because it is only 1 proton and 1 electron (no neutrons)

• Its properties are closer to a nonmetals than to a metal

• it is a colorless, odorless, explosive gas with oxygen

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ALKALINE-EARTH METALS

• Group 2

• 2 valence e- ’s

• Silver colored, more dense metals

• Not as reactive as alkali metals, but still very reactive metals.

• Magnesium is used in flash bulbs

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TRANSITION METALS• Groups 3-12 • 1 or 2 valence e- ’s• Most are silver in color• Somewhat reactive• These are most metals

you are familiar with• iron, gold, copper,

zinc and nickel• Since they are not that

reactive they have more everyday uses.

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TRANSITION METALS

• Two bottom rows are the Lanthanide and Actinide series, sometimes called innertransition metals

• Lanthanide: also called rare-earth metals

• Actinide: very radioactive and not easily found in nature

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NONMETALSHalogens, Noble Gases

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HALOGENS• Group 17/7a• 7 valence e- ’s• All nonmetals (can be

solid, liquid or gas)• Extremely reactive with

alkali metals• Chlorine is added to

water as a disinfectant.• The “chlorine” added to

pools is a compound containing Chlorine, by itself chlorine is a green gas

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NOBLE GASES• Group 18/8a

• 8 valence e- ’s (except Helium)

• Full outer shell of electrons

• All are gases

• Extremely non-reactive (inert)

• All found in the atmosphere

• “Neon” lights contain a variety of Noble Gases

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OTHER NONMETALS AND METALLOIDS

• Groups 13-16 contain both nonmetals and metalloids• Nonmetals: Oxygen, Nitrogen, Carbon,

Sulfur, Phosphorus, and Selenium

• Metalloids: Boron, Silicon, Germanium, Arsenic Antimony, and Terellium

• The group is named by the first element in the column 42

BORON GROUP

• Group 13

• 3 valence e- ’s

• 1 metalloid, all others are metals

• All are solids at room temperature

• Aluminum is the most common

• it is actually the most abundant element on the planet. 43

CARBON GROUP

• Group 14• 4 valence e- ’s• 1 nonmetal, 2 metalloids, 2 metals• all are solids• Pure carbon can be diamonds, soot (ashes)

or graphite.• Silicon and germanium are used for

computer chips• Tin and lead are common metals 44

NITROGEN GROUP

• Group 15

• 5 valence e- ’s

• 2 nonmetals, 2 metalloids, 1 metal

• All but nitrogen are solids

• Nitrogen makes up 78% of the air

• Phosphorus is in several compounds (soaps)

• Arsenic is a well known poison45

OXYGEN GROUP

• Group 16

• 6 valence e- ’s

• 3 nonmetals, 2 metalloids

• except oxygen, all are solid

• Oxygen makes up 21% of the air

• it is necessary for things to burn

• sulfur is a yellow rock, that can burn. 46