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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.
www.chem4kids.com
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
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
•