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Periodic Table and Trends
Essential Question:
How can we use the trends of
the periodic table to know more
about chemical interactions?
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The Periodic Table
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Periodic Table
Elements classified by:
properties
 atomic number (protons)
Groups (vertical) – have
similar chemical properties
1 = alkali metals
2 = alkaline earth metals
17 = halogens
18 = noble gases
Periods (horizontal)
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• Metals
– are on left of stair step line
– form positive ions in compounds
– form ionic bonds in compounds
• Non-metals
–
–
–
–
Are to right of stair step line
Form negative ions in compounds
Form ionic bonds with metals
Form covalent bonds with other non-metals
• Metalloids
– Are touching the stair step line
– Have properties of both metals and non-metals
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• Physical state of the elements:
– Solids are black on PT (all metals except for
mercury)
– Liquids are blue on PT (mercury and bromine)
– Gases are red on PT (H2 , N2 , O2 , F2 , Cl2 , He,
Ne, Ar, Kr, Xe, Rn)
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• Diatomic – exists as a molecule with 2
identical atoms
– 7 diatomics (they form a “7” in the PT)
• N2 , O2 , F2 , Cl2 , Br2 , I2 , and H2
• Monatomic – exists as a “molecule” that is
a single atom
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Dalton’s Atomic Theory (1808)
 Each element is made up of tiny particles
called atoms.
 The atoms of a given element are
identical; the atoms of different elements
are different in some fundamental way or
ways.
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Dalton’s Atomic Theory
(continued)
 Chemical compounds are formed when
atoms combine with each other. A given
compound always has the same relative
numbers and types of atoms.
 Chemical reactions involve reorganization
of the atoms - changes in the way they are
bound together. The atoms themselves are
not changed in a chemical reaction.
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Chemical Bonds
•The forces that hold atoms together in
compounds.
•Covalent bonds: result from atoms sharing
electrons.
–Molecule: a collection of covalently-bonded
atoms.
•Ionic bonds: result from + and – attraction
Electrons are NOT shared
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The Chemists’ Shorthand:
Formulas
• Chemical Formula:
•
Symbols = types of atoms
•
Subscripts = relative numbers of atoms
CO2
• Structural Formula:
•
Individual bonds are shown by lines.
O=C=O
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The
structural
formula
for
methane.
Space-filling model of methane. This
type of model shows both the relative
sizes of the atoms in the molecule and
their spatial relationships.
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Ball-and-stick model of methane.
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Early Experiments to
Characterize the Atom

J. J. Thomson - postulated the existence of
electrons using cathode ray tubes.

Ernest Rutherford - explained the nuclear
atom, containing a dense nucleus with
electrons traveling around the nucleus at a
large distance. Gold Foil Experiment
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Deflection of cathode rays by an
applied electric field.
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Rutherford's experiment on
-particle bombardment of metal foil.
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The Modern View of Atomic
Structure
The atom contains:

electrons

protons: found in the nucleus, they have a
positive charge equal in magnitude to the
electron’s negative charge.

neutrons: found in the nucleus, virtually
same mass as a proton but no charge.
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The Mass and Change of the
Electron, Proton, and Neutron
Particle
Mass (kg)
Charge
Electron
9.11  1031
1
27
Proton
1.67  10
Neutron
1.67  1027
1+
0
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The Chemists’ Shorthand: Atomic
Symbols
Mass number 
Atomic number 
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K
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 Element Symbol
Mass number = protons + neutrons
Atomic number = protons (determines what the element is)
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Isotopes – same element, different mass
- same number of protons
- different number of neutrons
-
++
+
-
+
+
+
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Two isotopes of sodium. Both have eleven
protons and eleven electrons, but they differ in
the number of neutrons in their nuclei.
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Give the number of protons and neutrons and electrons
in each:
25Mg
37Cl
195Pt
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Identify the element and write the symbol that has:
28 protons and 30 neutrons
55 protons and 78 neutrons
Atomic#=47 and Mass#=108
Z=9 and A=19
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The Periodic Table
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Ions
Cation: A positive ion
Mg2+, NH4+
Anion: A negative ion
Cl, SO42
Ionic Bonding: Force of attraction between
oppositely charged ions.
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28
++
+
-
++
+
-
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Formation of ions
How many electrons are lost or gained to
form the ions?
1. Na+
2. F3. Mg2+
4. O25. N330
Sodium metal reacts with chlorine gas to
form solid sodium chloride.
Average Atomic Masses
• Elements occur in nature as mixtures of
isotopes
• We do a “weighted average” to find the
average mass
• Carbon =
98.89% 12C
1.11% 13C
<0.01% 14C
• Carbon atomic mass = 12.01 amu
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Mass
spectrum
of natural
copper.
Calculate the average mass of gallium. Gallium
consists of one isotope mass 68.95 amu (60.16%)
and another isotope 70.95 amu (39.84%).
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Finding Chemical Formulas
1. You have to know the charge of each
element in the compound.
2. Get the charge of an element by looking at
the periodic table group
3. Use the criss-cross method
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What is the chemical formula for a
compound made of Ca and Cl?
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Charge states for groups
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Find the chemical formulas for:
1. Mg and F
2. K and S
3. Ca and O
4. Li and P
5. Cs and Br
6. Ba and N
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