CHAPTER 2 Atoms and the Periodic Table General, Organic, & Biological Chemistry Janice Gorzynski Smith

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

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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

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Matter Definition

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Matter Compounds


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


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:





Opposite charges attract while like chargesrepel each other.

Protons and electrons attract each other, buttwo electrons repel each other.



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



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 neutronsMass number (A) =

# of protons = 17

# of electrons = 17

# of neutrons = 35 – 17 = 18

Atoms Atomic Weight


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


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


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.


Periodic Table

Elements

18

Periodic Table

Elements


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


Periodic Table

Metals, Nonmetals, Metalloids

Periodic Table

Metals, Nonmetals, Metalloids


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


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





25http://chemwiki.ucdavis.edu/

Atoms Valence Electrons


•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.



•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.



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



•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


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


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.

CHAPTER 2 Atoms and the Periodic Table General, Organic, & Biological Chemistry Janice Gorzynski Smith

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