Chemistry I

Unit III

The atom & the periodic table

Ms. Claudia Barahona

October 2014

Stage 3

• Development of atomic theories

• Subatomic particles

• Electron configuration

• Organization of elements on the

periodic table

• Periodic properties (trends):

– Atomic size

– Ionization energy

– Electronegativity

Activity 3.1 The atom

• What is the atom composed of?

• Composed by subatomic particles:

• Protons : p+

• Electrons: e-

• Neutrons: n

Subatomic particles

• Particles that are smaller than the atom.

• Protons and neutrons make up the nucleus of an atom.

Note: Amu (Atomic Mass Unit) is defined as one-twelfth of the mass of

the carbon atom with six protons and six neutrons.

Name Symbol Elctrical charge Mass (amu)

Proton

Electron

Neutron

Name Symbol Elctrical charge Mass (amu)

Proton p+

Electron e-

Neutron n

Name Symbol Elctrical charge Mass (amu)

Proton p+ +1 1

Electron e- -1 0.000549

Neutron n 0 1

• Atomic number:

Is equal to the number of p+ in an atom.

• Mass number:

Is equal to the number of p+ and n in

the nucleus of an atom.

• Atomic mass or atomic weight:

Weight average mass of all the

natural occuring isotopes of an element

Information in the periodic table

Smallest particle of an element that retains the characteristis of

the element.

Atom

Atomic theories: Theories that try to explain the structure of the atom:

• Dalton

• Thomson

• Bohr

• Ruhtherford

• Schrodinger

• Decomposition process in which unstable atomic nuclei will spontaneously decompose to form nuclei with a higher stability, resulting in a release of high energy radiation.

Radioactivity

Radioactivity

Benefits Risk

Used in nuclear medicine. Radiotheraphy Irradiation

Can burn the surface of the skin. In contact with cells in the body may cause genetics mutations.

Fire detective systems Generates wastes which we do not know how to manage or destroy. Nuclear power stations

• Ex: P-32 (Tx of Leukemia), C-14 (Radiocarbon dating),

Au-198 (Liver imaging and carcinoma), I-123 (Thyroid, brain and porstate cancer).

Modern periodic table

• Period: Each horizontal row.

• Group/family: Each vertical column, this elements will have similar properties.

Modern periodic table

Representative elements

Transition Metals

Periodic trends

Representative elements

Transition Metals

Acquisition of knowledge

• Isotopes:

Are atoms of the same element that have different mass number but the same chemical behavior.

Atomic symbol for writing Isotopes: AZX X= chemical symbol for the element Z= Atomic number A= Mass number

• Atomic mass or atomic weight: Weight average

mass of all the natural occuring isotopes

of an element

• Atomic number: Is equal to the number

of protons in an atom.

Information in the periodic table

Representative elements

Transition Metals

Exercise # 1 Subatomic particles

• Is each of the following statements true or false?

If false, explain your reason.

a. Protons are heavier than electrons.

True

b. Protons are attracted to neutrons.

False. p+ are attracted to e-

c. Electrons are so small that they have no electrical charge.

False. e- have a -1 charge

d. The nucleus contains all the protons and neutrons of an atom.

True

Exercise # 2 Subatomic particles

• Using the periodic table, state the atomic number, number of protons, and number of electrons for an atom of each of the following elements:

Element Atomic

number p+ e-

Nitrogen

Magnesium

Bromine

Representative elements

Transition Metals

Subatomic particles

• Using the periodic table, state the atomic number, number of protons, and number of electrons for an atom of each of the following elements:

Element Atomic

number p+ e-

Nitrogen 7 7 7

Magnesium 12 12 12

Bromine 35 35 35

Exercise # 3 Subatomic particles

• Consider an atom that has 79 electrons.

a. How many protons are in its nucleus?

b. What is its atomic number?

c. What is its name, and what is its symbol?

Representative elements

Transition Metals

Subatomic particles

• Consider an atom that has 79 electrons.

a. How many protons are in its nucleus?

79

a. What is its atomic number?

79

a. What is its name, and what is its symbol?

Subatomic particles

• The number of protons gives atoms their identity.

• Atomic number (Z)

#of protons

• Mass number (A)

• #protons + #neutrons

Information in the periodic table

• Atomic mass or atomic weight: Weight average

mass of all the natural occuring isotopes

of an element.

• Isotopes:

Are atoms of the same element that have different mass number but the same chemical behavior.

Atomic symbol for writing Isotopes: AZX X= chemical symbol for the element Z= Atomic number A= Mass number

Identify protons and neutron in isotopes

State the number of p+, e- and n in each of the following isotopes of Carbon (C).

Exercise# 4 Isotopes

Isotope Protons Electrons Neutrons Protons Electrons Neutrons

6 6 6

6 6 7

6 6 8

Identify protons and neutron in isotopes

Write the symbol for each of the following isotopes:

a) A nitrogen atom with 8 neutrons.

b) An atom with 20 protons and 22 neutrons.

c) An atom with mass number 27 and 14 neutrons.

Exercise# 5 Isotopes

Representative elements

Transition Metals

Write the symbol for each of the following isotopes:

a) A nitrogen atom with 8 neutrons.

157N

a) An atom with 20 protons and 22 neutrons. 42

20Ca

a) An atom with mass number 27 and 14 neutrons.

2713Al

Exercise# 5 Isotopes

Review activity 3.2

Atomic theories

• Theories that try to explain the

structure of the atom.

– John Dalton

– J. J. Thomson

– Ernest Rutherford

– Niels Bohr

– Erwin Schrodinger

Evolution of the atomic theories

Billiard ball model- a small, solid sphere

Evolution of the atomic theories

Law of Conservation of mass:

States that the total mass present before a chemical reaction

is the same as the total mass present after the chemical

reaction; thus, mass is conserved. The law of conservation

of mass was formulated by Antoine Lavoisier (1743-1794).

This law was a result of his combustion.

Evolution of the atomic theories

Law of Constant composition or Law of definite

proportions:

Formulated by Joseph Proust (1754-1826).

States that if a compound is broken down into its constituent

elements, the masses of the constituents will always have

the same proportions, regardless of the quantity or source of

the original substance.

Evolution of the atomic theories

Law of Constant composition or Law of definite

proportions:

Jon Berzelius did experiments with about 2000 compounds

Berzelius prepared and purified the necessary reagents,

developed the techniques to perform the analyses, and

collected data on the relative weights of atoms of 43

elements.

That confirmed John Dalton's atomic theory as well as

Proust's law showing that separate elements always

combined in whole-number proportions.

*Also introduced the symbolism with which chemical

formulas are still written

Evolution of the atomic theories

How was Dalton wrong in his proposal?

Not all atoms of the same element are exactly alike

(isotopes).

Atoms are made up of subatomic particles.

J.J. Thomson

• Discovered the electron in a series of experiments using cathode-ray tube.

• In 1904 Thomson suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces.

“Plum-pudding”

model

Ernest Rutherford • Rutherford performed a series of experiments

with radioactive alpha particles.

• He found that while most of the alpha particles passed right through the gold foil, a small number of alpha particles passed through at an angle (as if they had bumped up against

something) and some bounced straight

back

• Rutherford's experiments suggested

that gold foil, and matter in general, had

holes in it!

Niels Bohr

• Devised the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system.

Erwin Schrodinger

• Schrödinger model describes the probability that an electron can be found in a given region of space at a given time. This model no longer tells us where the electron is; it only tells us where it might be.

• Introduced “wave

mechanics” as a

mathematical model.

Evolution of the atomic theories

Evolution of the atomic theories

Electronic configuration

Energy level: Specific energy that an electron has (bound by the electric field of the nucleus).

e- in the lower energy levels are usually closer

to the nucleus.

Sublevel: Group of orbitals of equal energy within principal energy level.

Orbital: Region around the nucleus where e-s of a certain energy are more likely to be found. (s, p,d and f)

Electronic configuration

List of the number of electrons in each sublevel within an atom, arranged by increasing energy.

Electronic configuration

Orbital´s maximum number of e-

• S= 2

• P= 6

• d= 10

• f = 14

Electronic configuration

Representative elements

Transition Metals

Electronic configuration

• To contruct the electronic configuration of an atom do the following:

1. Determine the number of electrons in the atom.

2. Put electrons moving from the lowest energy levels to the highest energy orbital available, starting with 1s (holds a maximum of two electrons).

3. Fill in the orbitals according to the number of electrons in the atom.

Electronic configuration

• Example: Write the electronic configuration of Lithium atom.

1. Electrons involved:

atomic number 3

2. Begin with the 1s sublevel.

1s2

3. Fill in the needed orbitals, until all the electrons are being positioned.

1s2 2s1

Electronic configuration

• Write the electron configuration for :

a. Nitrogen atom

b. Silicon atom

c. Chlorine atom

Representative elements

Transition Metals

Electronic configuration

• Write the electron configuration for :

a. Nitrogen atom

1s2 2s2 2p3

b. Silicon atom

1s2 2s2 2p6 3s2 3p2

c. Chlorine atom

1s2 2s2 2p6 3s2 3p5

Electronic configuration

• List of the number of electrons in each sublevel within an atom, arranged by increasing energy.

• Chemistry book chapter 3 Pg 81

Orbital diagram

• Boxes represent the orbitals and half arrows represent electrons.

Electronic configuration

Maximum number of e-

• S= 2

• P= 6

• d= 10

• f = 14

Aufbau´s principle

• e-s fill orbitals starting at the lowest available energy state before filling higher states (1s before 2s).

Pauli exclusion principle

• States the an orbital can hold up to maximum of 2 e-´s, which are seeing as spinning on its axis, which generates a magnetic field.

• An orbital can hold 0, 1, or 2 electrons only, and if there are two electrons in the orbital, they must have opposite (paired) spins.

Hund´s rule

• When filling sublevels other than s, electrons are placed in individual orbitals before they are paired up.

Representative elements

Transition Metals

Blocks in the periodic table

Valence electrons

• Electrons in the outermost energy level.

• Given by the group number (representative elements).

Valence electrons

• Electrons in the outermost energy level.

• Given by the group number (representative elements).

Oxidation number

• Shows the total number of e-´s which have been removed from an element (+) or added to an element (-).

Periodic trends

• Elctron configuration of atoms are an important factor in physical and chemical properties of the elements.

• Periodic properties increases or decreases across a period, and then the trend is repeated again in each successive group.

Periodic trends

• Electron afinity: The ability of an atom to attract additional electrons.

• Electronegativity: The relative ability of an element to attract electrons in a bond.

• Ionization energy: Energy needed to remove the least tight bound electron from an atom in gaseous (g) state.

• Atomic radius: Distance from the nucleus to the energy level that contains the valence (outermost) electrons.

Periodic trends

Writing formulas

1. Identify the cation and anion or polyatomic ion.

2. Balance the charge.

3. Write the formula, cation first, using the subscript from the charge balance.

Subscripts in formulas

• The subscripts in the formula represent the number of positive and negative ions that give an overall charge of zero.

Check activity 3.3

Check End of chapter