Chapter 3Elements and the Periodic Table

Structure of an AtomNucleus: small center core of an atom.

+ ++

Nucleus

e -Protons: positively charged atomNeutrons: particles with no charge

•Protons and neutrons have about equal mass •Together the protons and neutrons make up most of the atoms mass.

Electrons: negatively charged particles that move rapidly around the nucleusElectron cloud: the space around the nucleus where the electrons are located.

oAccounts for most of the atoms volume.

• Electrons have the smallest mass• They have distinct amounts of energy ….

higher energy electrons are farther away from the nucleus

Lower energy electrons are closer to the nucleus.

• In an atom: the number of protons = the number of electrons.

• The number of neutrons can be different.

Elements can be identified by the number of protons in the nucleus of its atom.

• Atomic Number: the number of protons in its nucleus.– The number of protons identifies

the atom.– Example: Oxygen has an atomic

number of 8

• Mass Number: the sum of the protons and neutrons in the nucleus of an atom.

8O

Oxygen15.999

To determine the number of neutrons in an atom:

Mass Number – Atomic Number = # of Neutrons.

Example: Lithium has an atomic number of 3 and a mass number of 6.941 which we round to 7.

3Li

Lithium6.941Mass Number – Atomic Number = # of Neutrons

7 - 3 = 4 NeutronsTherefore…. Lithium has: 3 protons and 4 neutronsWhat about electrons??????Remember: neutral atoms (atoms with no charge) have an equal number of protons and electrons……Therefore..... Lithium has: 3 electrons.

Element Symbol Atomic # Atomic Mass

Protons Neutrons Electrons

Lithium Li 3 7 3 4 3

Phosphorous P 15 31 15 16 15

Chlorine Cl 17 35 17 18 17

Potassium K 19 39 19 20 19

Silver Ag 47 108 47 61 47

Silicon Si 14 28 14 14 14

Hydrogen H 1 1 1 0 1

Isotopes:

• Atoms that have the same number of protons but different numbers of neutrons.

– Example: Carbon always has 6 protons, but may have 6, 7, or 8 neutrons.

• Common notations for isotopes of Carbon with 8 neutrons are C-14, Carbon- 14 or 14C

Bohr Model

• A model used to show energy levels and where electrons may be located around the nucleus.

• The energy level closest to the nucleus holds 2 electrons

• The next energy level holds 8 electrons.• The third energy level can hold up to 18

electrons. • The last energy level holds electrons called

valence electrons

To Draw a Bohr Diagram:

• Find your element on the periodic table.• Inside the nucleus write the number of

protons and number of neutrons (determine by subtracting atomic number and atomic mass.)

• Determine the number of electrons – it is the same as the atomic number.

• This is how many electrons you will draw.

• Carbon has an atomic number of 6• You will draw 6 electrons.• Remember your rules, the first shell can only

have 2 electrons.• The remaining 4 electrons will go into the next

energy level.

6 P6 N

Valence electrons

• the outermost electrons from the nucleus.• The number of valence electrons give the

element its chemical properties. • The greatest number of valence electrons for

any atom is 8.• These electrons play a role in chemical

bonding between atoms to form molecules.

Organizing Elements

Dmitri Mendeleev

• a Russian scientist who discovered a set of patterns that applied to all the elements.

• He noticed a pattern or properties appeared when he arranged the elements in order of increasing atomic mass.

The Modern Periodic Table

• New elements have been added since Medeleev’s table.

• Elements are arranged in order of increasing atomic number

• Contains one square for each element

26Fe

Iron55.847

Atomic Number

Symbol

Element

Atomic Mass Number

The Properties of an element can be predicted from its location in the periodic table.

Periods: the horizontal rows(colored pink)

- Numbered 1-7- The elements have the same # of valence shells.

Across the Periodic Table• Periods: Are arranged horizontally across the periodic

table (rows 1-7)• These elements have the same number of valence shells.

1IA

18VIIIA

1 2IIA

13IIIA

14IVA

15VA

16VIA

17VIIA

2

3 3IIIB

4IVB

5VB

6VIB

7VIIB

8 9VIIIB

10 11IB

12IIB

4

5

6

7

2nd Period

6th Period

Groups: the vertical columns (colored blue)– Also called families– Elements have similar

characteristics– Numbered 1-18– The number of valence electrons is the same for all elements in a group

Down the Periodic Table•Family: Are arranged vertically down the periodic table (columns or group, 1- 18 or 1-8 A,B)•These elements have the same number electrons in the outer most shells, the valence shell.

1IA

18VIIIA

1 2IIA

13IIIA

14IVA

15VA

16VIA

17VIIA

2

3 3IIIB

4IVB

5VB

6VIB

7VIIB

8 9VIIIB

10 11IB

12IIB

4

5

6

7

Alkali Family: 1 e- in the valence shell

Halogen Family: 7 e- in the valence shell

Lewis Structures

1) Find your element on the periodic table.2) Determine the number of valence electrons.3) This is how many electrons you will draw.

Lewis Structures

• Find out which group (column) your element is in.

• This will tell you the number of valence electrons your element has.

• You will only draw the valence electrons.

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GroupsGroup 1 = 1 electron

Group 2 = 2 electrons

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Group 13 = 3 veGroup 14 = 4 veGroup 15 = 5 veGroup 16 = 6 veGroup 17 = 7 veGroup 18 = 8 ve (except He)

Lewis Structures1) Write the element

symbol.2) Carbon is in the 14th

group, so it has 4 valence electrons.

3) Starting at the right, draw 4 electrons, or dots, counter-clockwise around the element symbol.

C

Lewis Structures

C

1) Check your work.2) Using your periodic

table, check that Carbon is in the 14th group.

3) You should have 4 total electrons, or dots, drawn in for Carbon.

Li

Ne Mg

Cl

Periodic Table: Metallic arrangement• Layout of the Periodic Table: Metals vs. nonmetals

1IA

18VIIIA

1 2IIA

13IIIA

14IVA

15VA

16VIA

17VIIA

2

3 3IIIB

4IVB

5VB

6VIB

7VIIB

8 9VIIIB

10 11IB

12IIB

4

5

6

7

MetalsNonmetals

Infamous Families of the Periodic Table• Notable families of the Periodic Table and some important members:

1IA

18VIIIA

1 2IIA

13IIIA

14IVA

15VA

16VIA

17VIIA

2

3 3IIIB

4IVB

5VB

6VIB

7VIIB

8 9VIIIB

10 11IB

12IIB

4

5

6

7

Alkali

Alkaline (earth)

Transition Metals

Noble GasHalogen

Chalcogens

Properties of Metals

• Shiny• Malleable : can be hammered or rolled into flat

sheets and other shapes• Ductile: can be pulled out or drawn into a long wire.• Conductive: the ability of an object to transfer heat

or electricity to another object. • Reactive: they combine or react with other elements

easily. – A chemical property of metal is its reaction with water

which results in corrosion.

Alkali metals:• metals in Group 1• Hydrogen is NOT a member (it is not a metal)• React with other elements by losing one electron.• So reactive that they are never found uncombined in

nature. They are only found in compounds.• Very reactive with water.• Shiny and soft so that you can cut with a knife.• Examples: sodium (Na), Lithium (Li), Potassium (K)

Alkaline Earth Metals:• metals in Group 2• Fairly hard, gray-white metals• Good conductors of electricity• React by losing 2 electrons• Not as reactive as Group 1

elements– Never found uncombined in nature.– Examples: beryllium, magnesium,

calcium, barium

Transition metals

• Groups 3 – 12• Most are hard and shiny• Good conductors of electricity• Less reactive then group 1 and 2• Examples: Iron, copper, nickel,

gold, silver

Metals in Groups 13-15

• Not as reactive as metals on the right side of the periodic table.

• Aluminum, tin, lead

• Lanthanides• Top row on bottom of periodic table• Soft, malleable, shiny, high conductivity• Usually mixed with other elements to form

alloys: a mixture of metal with at least one other element.

Actinides: • Bottom row of bottom of periodic table• Some are created in a lab.• Some exist in nature

Nonmetals:• element that lacks most of the properties of a metal

Physical Properties• Poor conductors of electricity and heat• Reactive with other elements • Solid nonmetals are dull and brittle, not malleable and ductile• Have lower densities than metals• 10 of the 16 are gases at room temperature Chemical Properties• Reactive and gain or share electrons when they react with

other atoms.

Metalloids:

• elements that have characteristics of both metals and nonmetals

Properties (physical and chemical) • All are solid at room temperature• Brittle, hard and somewhat reactive• Most useful property is their varying ability to conduct

electricity.– Used to make semiconductors: substances that can

conduct electricity under some conditions but not under other conditions. Used to make computer chips, lasers and transistors

http://library.thinkquest.org/3659/pertable/metaloid.map

BORON FAMILY

Group 13• 3 valence

electrons in the outer shell

• Most are metals: Aluminum, Gallium, Indium Thallium

• Metalloid: Boron

CARBON FAMILY Group 14• 4 valence electrons• Atoms can gain, lose

or share 4 electrons• Non-metal: Carbon

(C)• Metalloids: silicon,

germanium• Metals: Tin and

lead

NITROGEN FAMILY Group 15• 5 valence electrons in

the outer shell• Can gain or share 3

electrons to form compounds

• Non-metals: Nitrogen, phosphorous,

• Metalloids: arsenic, antimony

• Metals: bismuth

OXYGEN FAMILY Group 16• 6 valence electrons

in the outer shell• Can gain or share 2

electrons• Reactive• Nonmetals: Oxygen,

sulfur, selenium• Metalloids:

Tellurium Polonium• Metals: none

Halogens (salt forming)Group 17• 7 valence electrons in

the outer shell• Can gain or share 1

electron• Very reactive are often

bonded with elements from Group 1

• Nonmetals: Flourine, chlorine, bromine, iodine

• Metalloids: Astatine• Metals: none

Noble GasesGroup 18Exist as gases8 valence electrons in

the outer shell = FullHelium (He) has only 2

electrons in the outer shell = Full

Not reactive with other elements

Non-metals: Helium, neon, argon, krypton, xenon, radon

No metalloids or metals

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