CHAPTER 2 Atoms and the Periodic Table General, Organic, & Biological Chemistry Janice Gorzynski...
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Transcript of CHAPTER 2 Atoms and the Periodic Table General, Organic, & Biological Chemistry Janice Gorzynski...
CHAPTER 2Atoms and the Periodic Table
General, Organic, & Biological Chemistry
Janice Gorzynski Smith
2
CHAPTER 2: Atoms & the Periodic Table
Smith. General Organic & Biolocial Chemistry 2nd Ed.
Learning Objectives: Elemental Symbols
Metals vs Nonmetals vs Metalloids or Semimetals
Subatomic Particles: properties & location
Formulae of Compounds
Models to represent particles
Nucleus and structure of atom
Atomic number, Mass Number, Isotopes, Atomic Weight, & Atomic Mass
Periodic Table: groups & periods: similar properties within groups
Electron structure: valence electrons and electron dot symbols
Periodic trends: atomic size and ionization energy
3
Matter Definition
http://ridenourmhs.wikispaces.com/ESUnit2
Matter Elements
4Smith. General Organic & Biolocial Chemistry 2nd Ed.
•An element is a pure substance that cannot be broken down into simpler substances by a chemical reaction.
•Each element is identified by a one- or two-letter symbol.
•Elements are arranged in the periodic table.
•The position of an element in the periodic table tells us much about its chemical properties.
diamond = carbon gold sulfur
5
Matter Definition
http://ridenourmhs.wikispaces.com/ESUnit2
Matter Compounds
6Smith. General Organic & Biolocial Chemistry 2nd Ed.
Compound: a pure substance formed by chemically combining two or more elements together.
• Element symbols to show the identity of the elements forming a compound.
A chemical formula consists of:
• Subscripts to show the ratio of atoms in the compound.
H2O
2 H atoms 1 O atom
C3H8
3 C atoms 8 H atoms
H2O C3H8
Matter Compounds
7Smith. General Organic & Biolocial Chemistry 2nd Ed.
Compounds can be drawn many ways:
Different elements are represented by different colors:
Matter Depicting Compounds
8
H C H
H
H
CH4
methane
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Atoms Subatomic Particles
9Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
All matter is composed of the same basic building blocks called atoms.
Atoms are composed of three subatomic particles:
Atoms Subatomic Particles
10Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Atoms Subatomic Particles
11Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Opposite charges attract while like chargesrepel each other.
Protons and electrons attract each other, buttwo electrons repel each other.
Atoms Subatomic Particles
12Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
From the periodic table:
3Li
Atomic number (Z) is the number of protonsin the nucleus.
•Every atom of a given element has the same number of protons in the nucleus.
•Different elements have different atomic numbers.
•A neutral atom has no net overall charge, so
Z = number of protons = number of electrons
Atoms Subatomic Particles
13Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Isotopes are atoms of the same element that havea different number of neutrons.
35
17Cl
Mass number (A)
Atomic number (Z)
the number of protons (Z)+
the number of neutrons
Mass number (A) =
# of protons = 17
# of electrons = 17
# of neutrons = 35 – 17 = 18
Atoms Atomic Weight
14Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
The atomic weight is the weighted average of the masses of the naturally occurring isotopes of a particular element reported in atomic mass units.
From the periodic table:
6
C12.01
atomic number
element symbolatomic weight (amu)
Atoms Determine the Atomic Weight of an Element
15Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Example
Step [1]
What is the atomic weight of chlorine?
List each isotope, it’s mass in atomic mass units, and it’s abundance in nature.
Mass (amu) Isotopic AbundanceIsotope
Cl-35
Cl-37
34.97
36.97
75.78% = 0.7578
24.22% = 0.2422
Atoms Determine the Atomic Weight of an Element
16Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Step [2]
Multiply the isotopic abundance by the massof each isotope, and add up the products.
34.97 x 0.7578
36.97 x 0.2422
=
=
26.5003 amu
8.9541 amu
35.4544 amu = 35.45 amu
Answer4 sig. figs.
The sum is the atomic weight of the element.
4 sig. figs.
17Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Periodic Table
Elements
18
Periodic Table
Elements
19Smith. General Organic & Biolocial Chemistry 2nd Ed.
1A 2A B B 7A 8A
Alkali Metals Alkaline Earth
Metals
Transition Metals
Lanthanide & Actinide
Halogens Nobel Gases
Very reactive
Metals except for H
+1 ions
React with Oxygen to form compounds that dissolve into alkaline solutions in water
Reactive
+2 ions
Oxygen compounds are strongly alkaline
Many are not water soluble
Metals
Form ions with several different charges (oxidation states)
Tend to form +2 and +3 ions
Lanthanides 58 – 71
Actinides 90 – 103
Actinides are radioactive
Reactive
Form diatomic molecules in elemental state
-1 ions
Salts with alkali metals
Inert
Heavier elements have limited reactivity
Do not form ions
Monoatomic gases
Periodic Table
Groups
20Smith. General Organic & Biolocial Chemistry 2nd Ed.
Periodic Table
Metals, Nonmetals, Metalloids
Periodic Table
Metals, Nonmetals, Metalloids
21Smith. General Organic & Biolocial Chemistry 2nd Ed.
Metals Nonmetals Metalloids
• Metallic luster, malleable, ductile, hardness variable
• Conduct heat and electricity
• Solids at room temperature with the exception of Hg
• Chemical reactivity varies greatly: Au, Pt unreactive while Na, K very reactive
• Brittle, dull
• Insulators, non-conductors of electricity and heat
• Chemical reactivity varies
• Exist mostly as compounds rather then pure elements
• Many are gases, some are solids at room temp, only Br2 is a liquid.
• Properties intermediate between metals and nonmetals
• Metallic shine but brittle
• Semiconductors: conduct electricity but not as well as metals: examples are silicon and germanium
Atoms Carbon
22Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Carbon’s ability to join with itself and other elementsgives it a versatility not seen with any other element in the periodic table.
Elemental forms of carbon include the following carbon-only structures:
diamond graphite buckminsterfullerene
Atoms Electron Configurations & Orbitals
23Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Atoms Electron Configurations & Orbitals
24Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Atoms Electron Configurations & Orbitals
25http://chemwiki.ucdavis.edu/
Atoms Valence Electrons
26Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
•The valence shell is the outermost shell (the highest value of n).
Be
1s22s2
Cl
1s22s22p63s23p5
valence shell: n = 2
# of valence electrons = 2
valence shell: n = 3
# ofvalence electrons = 7
•The electrons in the valence shell are called valence electrons.
•The chemical properties of an element depend on the number of electrons in the valence shell.
Atoms Valence Electrons
27Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
•Elements in the same group have similar electron configurations.
•Elements in the same group have the same number of valence electrons.
•The group number, 1A–8A, equals the number of valence electrons for the main group elements.
•The exception is He, which has only 2 valence electrons.
•The chemical properties of a group are therefore very similar.
Atoms Valence Electrons
28Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Group number:
Period 1:
Period 2:
Period 3:
1A 2A 3A 4A 5A 6A 7A 8A
Li2s1
Be2s2
B2s22p1
C2s22p2
N2s22p3
O2s22p4
F2s22p5
Ne2s22p6
Na3s1
Mg3s2
Al3s23p1
Si3s23p2
P3s23p3
S3s23p4
Cl3s23p5
Ar3s23p6
H1s1
He1s2
Atoms Valence Electrons
29Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
•Dots representing valence electrons are placed on the four sides of an element symbol.
•Each dot represents one valence electron.
•For 1 to 4 valence electrons, single dots are used. With > 4 valence electrons, the dots are paired.
Element:
# of Valence electrons:
Electron-dot symbol:
H
1
C
4
O
6
Cl
7
H C O Cl
Atoms Periodic Trends
30Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
The size of atoms increases down a column, as the valence e− are farther from the nucleus.
•The size of atoms decreases across a row, as the number of protons in the nucleus increases, pulling the valence electrons in closer.
IncreasesDecreases
Atoms Periodic Trends
31Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Decreases
The ionization energy is the energy needed to remove an electron from a neutral atom.
Na + energyNa+ + e–
•Ionization energies decrease down a column as the valence e− get farther away from the positively charged nucleus.Increases
•Ionization energies increase across a row as the number of protons in the nucleus increases.