Learning Objectives: a. The model of atomic theory was 1 st proposed by John Dalton in 1803. b. Atoms are composed of protons, neutrons, and electrons

Learning Objectives:

a. The model of atomic theory was 1st proposed by John Dalton in 1803.

b. Atoms are composed of protons, neutrons, and electrons.

c. All atoms of the same element contain the same number of protons (and electrons) but may vary in the number of neutrons (isotopes).

d. Protons and neutrons are found inside the tiny but dense nucleus, whereas electrons are found in orbitals outside the nucleus.

e. The arrangement of electrons in the orbitals is called the electronic configuration and determines the chemistry of an atom.

f. The different types of atoms are called elements, which are arranged systematically in the periodic table.

g. Having eight valence electrons is particularly desirable (“the octet rule”).

a. The Atomic Theory Dalton’s Atomic Theory

1. All matter is composed of indivisible atoms.2. All atoms of one element are identical to each

other but different than the atoms of other elements.

3. Compounds are formed when atoms of different elements combine in whole number ratios.

4. Atoms are rearranged during chemical reactions but atoms cannot be created or destroyed.

John Dalton (1766-1844)

Definitions

Law of conservation of matter states that matter is neither lost nor gained during a chemical reaction.

Law of definite proportions states that in a compound, the constituent elements are always present in a definite proportion by weight.

Ex. 2H2 (g) + O2 (g) 2H2O(g)

2C(s) + O2 (g) 2CO(g)

Ex. Pure water, a compound, is always made up of 11.2% hydrogen and 88.8% oxygen by weight or table sugar always contains 42.1% carbon, 6.5% hydrogen, and 51.4% oxygen by weight.

b. Structure of the Atom Components

Positive protons, negative electrons, and neutral neutrons

Atomic Number The number of protons in an atom, which

determines what element it is Mass Number

Number of protons + the number of neutrons

Definitions

Protons are positively charged subatomic particles found in the nucleus.

Neutrons are electrically neutral subatomic particles found in the nucleus.

Electrons are negatively charged subatomic particles found in the space around the nucleus.

Nucleus is the small central core of the atom: contains the protons and neutrons.

Ernest Rutherford Gold foil experiment. A beam of positively charged alpha particles hits the gold foil. Most particles passed straight, some slightly deflected and some deflected back. The reason for deflection were the positions of the nucleus.

Separation of alpha, beta, and gamma particles by applying an electric field.

Ernest Rutherford (1871-1937)

Rutherford’s interpretation of the gold foil experiment done by Geiger and Marsden.

Modern View of the Atom

For an atom, which always has no net electrical charge, the number of negatively charged electrons around the nucleus equals the number of positively charged protons in the nucleus.

Scientists have been able to obtain computer-enhanced images of the outer surface of atoms using the scanning tunneling microscope (STM) and the atomic force microscope (AFM).

c. Structure of the Atom Isotopes

Isotopes of the same element have the same number of protons and electrons but differ in the number of neutrons.

Atomic Mass The atomic mass for each element on the

periodic table reflects the relative abundance of each isotope in nature.

DefinitionsAtomic number is the number of protons in the nuclei of the atoms of an element

Mass number or atomic mass is the number of neutrons plus number of protons in the nucleus of an atom

Mass number = #’s of protons + #’s of neutrons

Ex. How many protons, neutrons, and electrons are in atom of gold (Au) with a mass number of 197?

Protons = 79; Electrons = 79; Neutrons = 197 – 79 = 118;

Isotopes are atoms of the same element having different mass numbers.

Definitions cont

Atomic mass unit (amu) is the unit for relative atomic masses of the elements; 1 amu =1/12 the mass of carbon-12 isotope. 1 amu = 1.6605x10-24 grams

Atomic weight is the number that represents the average atomic mass of the element’s isotopes weighted by percentage abundance.

Isotopes

H1

1 H1

2 H1

3

Write the nuclear symbols for atoms with the following subatomic particles.

A. 8 p+, 8 n, 8 e- ___________

B. 17p+, 20n, 17e- ___________

C. 47p+, 60 n, 47 e- ___________

Learning Check

A. 8 p+, 8 n, 8 e- 16O

8

B. 17p+, 20 n, 17e- 37Cl 17

C. 47p+, 60 n, 47 e- 107Ag 47

Solution

Learning Check

1. Which of the following pairs are isotopes of the same element?2. In which of the following pairs do both atoms have 8 neutrons? A. 15X 15X 8 7

B. 12X 14X 6 6

C. 15X 16X 7 8

Solution

B. 12X 14X

6 6

Both nuclear symbols represent isotopes of carbon with six protons each, but one has 6 neutrons and the other has 8.

C. 15X 16X

7 8

An atom of nitrogen (7) and an atom of oxygen (8) each have 8 neutrons.

Isotopes of Magnesium

In naturally occurring magnesium, there are three isotopes.

24Mg 25Mg 26Mg 12 12 12

Isotopes of Mg

Relative Masses of Atoms

Use atomic weights of the elements to calculate molecular weights (MW) of compounds

Relative masses provide a simple way of comparing the masses of atoms. Ex. The mass of neon atoms is 20.18 and the mass of calcium atoms is 40.08.

Ca atom massNe atom mass

= 40.0820.18

= 1.986 Mass of Calcium is 2x than Ne

He atom mass H atom mass

= 4.0031.008

= 3.971 Mass of Helium is 4x than Hydrogen

The exact relationship between two masses calculated

Calculating the atomic weight of compounds MW = CnHmOk

MW = n(at. Wt. C) + m(at. Wt. H) + k(at. Wt. O)

H2O the MW is

MW = 2(at. Wt. H) + 1(at. Wt. O)

MW = 2(1.008 u) + 1(15.996 u)

MW = 18.012 u or 18.01 u for water

Use atomic weighs from the periodic table inside the front cover of your book to determine the molecular weight of urea, CH4N2O, the compound by which much nitrogenous body waste is excreted in the urine.

Learning Check

a. 58.02 u

b. 62.25 u

c. 60.06 u

Solution

MW = n(at. Wt. C) + m(at. Wt. H) + k(at. Wt. O)

The chemical formula for urea is CH4N2O,

MW = 1(12.01 u) + 4(1.008) + 2(14.01) + 1(16.00)

MW = 60.062 u or rounded off 60.06 u

d. Models of the Atom The Plum Pudding Model

Electrons are embedded in a sphere of positive charge.

The Nuclear Model All of the positive charge is in a tiny central

nucleus with electrons outside the nucleus. This model was developed by Rutherford

after his landmark experiments.

The Rutherford Experiment

e. Models of the Atom (continued) Bohr Model or the Solar System Model

Niels Bohr in 1913 introduced his model of the hydrogen atom.

Electrons circle the nucleus in orbits, which are also called energy levels.

An electron can “jump” from a lower energy level to a higher one upon absorbing energy, creating an excited state.

The concept of energy levels accounts for the emission of distinct wavelengths of electromagnetic radiation during flame tests.

Niels Bohr (1885-1962)

Bohr’s Orbit ModelDefinitions

Quantum is the smallest increment of energy, for example, in an atom emitting or absorbing radiation.

Ground state is the condition of an atom in which all electrons are in their normal, lowest energy levels.

Excited state is an unstable, higher energy state of an atom.

A line spectrum for hydrogen

Fig. 3-6a, p. 49

Neon (Ne)

Fig. 3-6b, p. 49

Neon, a partially evacuated tube that contains neon gas gives a reddish-orange glow when high voltage is applied.

The line emission spectrum of neon is obtained when light from a neon source passes through a prism.

Potassiumburns with a violet flame

Credit: Photo Researchers, Inc.

Lithium burns with a red flame

Electromagnetic Radiation

c = c is the speed of light is wavelength is frequency

Fig. 3-7, p. 50

It is important to understand E (for energy), wavelength, and frequency relationship:

As increases, and E decreases

As decreases, and E increases

Models of the Atom (continued) The Orbital Model

Orbits are replaced with orbitals, volumes of space where the electrons can be found.

The arrangement of electrons in the orbitals is the electronic configuration of an atom, which determines the chemistry of the atom.

Definitions

Electrons in the highest occupied energy level are the greatest stable distance from the nucleus. These outermost electrons are known as valence electrons.

Shell is a principal energy level defined by a given value of n, where n can be 1,2,3,4 etc… and is capable of holding 2n2 electrons.

An orbital is a region of three-dimensional space around an atom within which there is a significant probability (usually shown as 90%) that a given electron will be found.

Subshells have different energy levels (orbitals) within a given shell

Valence Electrons

The valence electrons • determine the chemical properties of the elements.• are the electrons in the highest energy level.• are related to the group number of the element.

Example: Phosphorus has 5 valence electrons. 5 valence electrons

P Group 5A(15) 2, 8, 5

All the elements in a group have the same number ofvalence electrons.

Example: Elements in group 2A(2) have two (2) valence electrons.

Be 2, 2Mg 2, 8, 2Ca 2, 8, 8, 2Sr 2, 8, 18, 8, 2

Groups and Valence Electrons

Periodic Table and Valence Electrons

Representative Elements Group Numbers

1 2 3 4 5 6 7 8

H He

1 2

Li Be Al C N O F Ne

2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8

Li Mg Ge Si P S Cl Ar

2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8

State the number of valence electrons for each.A. O

1) 4 2) 6 3) 8

B. Al

1) 13 2) 3 3) 1

C. Cl

1) 2 2) 5 3) 7

Learning Check

State the number of valence electrons for each.A. O

2) 6

B. Al

2) 3

C. Cl

3) 7

Solution

State the number of valence electrons for each.

A. 2, 8, 5

B. 2, 8, 8, 2

C. 2, 7

Learning Check

State the number of valence electrons for each.

A. 2, 8, 5 5

B. 2, 8, 8, 2 2

C. 2, 7 7

Solution

Energy levels are spaced differently, like ladder rungs

Credit: Foto-Search.com

Atomic energylevels are like floors of a house

State transitions for hydrogen

Table 3-2, p. 52

Fig. 3-8, p. 54

Atomic Orbitals.

Fig. 3-9, p. 55

The Orbital Model:Electronic Configurations

Sample energy level diagram

Table 3-3, p. 55

Fig. 3-10a, p. 56

Fig. 3-10b, p. 56

f. The Periodic Table Used to organize the elements by

recurring chemical properties. Elements in the same vertical column of

the periodic table have similar chemical properties and are said to be in the same group or family.

The Periodic Table Dmitri Mendeleev (1834-1907)

Groups and Periods

On the periodic table,

• elements are arranged according to similar properties.

• groups contain elements with similar properties in vertical columns.

• periods are horizontal rows of elements.

Groups and Periods

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Group Numbers

Group Numbers

• use the letter A for the representative elements (1A to 8A) and the letter B for the transition elements.

• also use numbers 1-18 to number the columns from left to right.

Names of Some Representative Elements

Several groups of representative elements are known by common names.


Alkali Metals

Group 1A(1), the alkali metals, includes lithium, sodium, and potassium.


Halogens

Group 7A(17) the halogens, includes chlorine, bromine, and iodine.


Identify the element described by the following.

A. Group 7A(17), Period 4 1) Br 2) Cl 3) Mn

B. Group 2A(2), Period 3 1) beryllium 2) boron 3) magnesium

C. Group 5A(15), Period 2 1) phosphorus 2) arsenic 3) nitrogen

Learning Check

A. Group 7A (17), Period 4 1) Br

B. Group 2A (2), Period 3

3) magnesium

C. Group 5A(15), Period 2

3) nitrogen

Solution

Metals, Nonmetals, and Metalloids

The heavy zigzag line separates metals and nonmetals.• Metals are located to the

left.• Nonmetals are located to

the right. • Metalloids are located

along the heavy zigzag line between the metals and nonmetals.


Comparing a Metal, Metalloid, and Nonmetal

Identify each of the following elements as

1) metal 2) nonmetal 3) metalloid

A. sodium ____

B. chlorine ____

C. silicon ____

D. iron ____

E. carbon ____

Learning Check

Identify each of the following elements as

1) metal 2) nonmetal 3) metalloid

A. sodium 1 metal

B. chlorine 2 nonmetal

C. silicon 3 metalloid

D. iron 1 metal

E. carbon 2 nonmetal

Solution

Match the elements to the description.

A. Metals in Group 4A(14) 1) Sn, Pb 2) C, Si 3) C, Si, Ge, Sn

B. Nonmetals in Group 5A(15) 1) As, Sb, Bi 2) N, P 3) N, P, As, Sb

C. Metalloids in Group 4A(14) 1) C, Si, Ge, 2) Si, Ge 3) Si, Ge, Sn, Pb

Learning Check

Match the elements to the description.

A. Metals in Group 4A (14)1) Sn, Pb

B. Nonmetals in Group 5A(15) 2) N, P

C. Metalloids in Group 4A(14) 2) Si, Ge

Solution

Fig. 3-11, p. 58

Table 3-4, p. 59

p. 60

Sulfur

CarbonGold

g. The Octet Rule The noble gases of Group VIIIA do not

typically form compounds with other atoms. Atoms with eight valence electrons are

particularly stable, an observation called the octet rule.

Atoms form bonds with other atoms to achieve a valence octet.

ElectronicConfiguration of Noble Gases

Lewis Dot Structures The number of valence electrons is equal to the

group number for most of the main group elements.

In Lewis dot structures, the chemical symbol represents the nucleus and the core electrons and dots represent the valence electrons.

Writing Electron-Dot Symbols

Electron-dot symbols for• groups 1A(1) to 4A(14) use single dots.

· · Na · · Mg · · Al · · C ·

·

• groups 5A(15) to 7A(17) use pairs and single dots. · · · ·

· P · : O · · ·

Groups and Electron-Dot Symbols

In a group, all the electron-dot symbols have thesame number of valence electrons (dots).

Example: Atoms of elements in Group 2A(2) each have 2 valence electrons.

· Be ·

· Mg ·

· Ca ·

· Sr ·

· Ba ·

Lewis Dot Structures

A. X is the electron-dot symbol for

1) Na 2) K 3) Al

B. X

is the electron-dot symbol of

1) B 2) N 3) P

Learning Check

A. X is the electron-dot symbol for

1) Na 2) K

B. X

is the electron-dot symbol of

2) N 3) P

Solution

Ionic Bonds Ionic compounds result from the loss of

electrons by one atom (usually a metal) and the gain of electrons by another atom (usually a nonmetal).

Ionic bonds arise from the attraction between particles with opposite charges (electrostatic forces); e.g., Na+ Cl-.

Ionic Compounds

Atomic Size

Atomic size is described using the atomic radius; the distance from the nucleus to the valence electrons.


Atomic Radius Within A Group

Atomic radius increases going down each group of representative elements.


Atomic Radius Across a Period

Going across a period left to right, • an increase in number of protons increases attraction for

valence electrons.• atomic radius decreases.


Learning Check

Select the element in each pair with the larger atomic

radius.

A. Li or K

B. K or Br

C. P or Cl

Solution

Select the element in each pair with the larger atomic

radius.

A. K

B. K

C. P

Key Words

Chemistry Matter Pure substance Mixture Element Compound Homogeneous mixture Heterogeneous mixture States of matter Solid

Liquid Gas Physical changes Chemical changes Atom Molecule Periodic table Periods Groups or Families Main group elements

Key Words (cont)

Transition elements Metals Nonmetals Semimetals Protons Neutrons Electrons Atomic number Mass number Isotopes Atomic Mass

Nucleus Electromagnetic radiation Wavelength Energy level Ground state Excited state Orbital Electronic configuration Valence electrons Outer shell

Documents

Learning Objectives: a. The model of atomic theory was 1 st proposed by John Dalton in 1803. b. Atoms are composed of protons, neutrons, and electrons