AtomsAtoms

Chapter 4Chapter 4

Section 1: “The Development of Section 1: “The Development of the Atomic Theory”the Atomic Theory”

The The atomatom is the smallest unit of all is the smallest unit of all matter.matter.

Section 1: “The Development of Section 1: “The Development of the Atomic Theory”the Atomic Theory”

Who: DemocritisWho: Democritis When: 4When: 4thth century B.C. century B.C. What: Suggested that What: Suggested that

the universe was made the universe was made of indivisible units.of indivisible units.

He called these units He called these units atomsatoms. “Atom” comes . “Atom” comes from from atomosatomos, a Greek , a Greek word that means “unable word that means “unable to be cut or divided.”to be cut or divided.”

Section 1: “The Development of Section 1: “The Development of the Atomic Theory”the Atomic Theory”

Who: John DaltonWho: John Dalton When: 1803When: 1803 What: Created the Atomic What: Created the Atomic

Theory:Theory:1.1. Every element is made of Every element is made of

tiny, unique particles called tiny, unique particles called atoms that cannot be atoms that cannot be subdivided.subdivided.

2.2. Atoms of the same element Atoms of the same element are exactly alike.are exactly alike.

3.3. Atoms of different elements Atoms of different elements can join to form molecules.can join to form molecules.

Section 1: “The Development of Section 1: “The Development of the Atomic Theory”the Atomic Theory”

Who: J.J. ThomsonWho: J.J. Thomson When: 1897When: 1897 What: Used a cathode-ray tube experiment to What: Used a cathode-ray tube experiment to

discover negatively charged subatomic particles called discover negatively charged subatomic particles called electrons.electrons.

Section 1: “The Development of Section 1: “The Development of the Atomic Theory”the Atomic Theory”

What: Proposed a new model of an atom called the What: Proposed a new model of an atom called the plum-pudding modelplum-pudding model..

Section 1: “The Development of Section 1: “The Development of the Atomic Theory”the Atomic Theory”

Who: Ernest RutherfordWho: Ernest Rutherford When: 1911When: 1911 What: Used the gold foil experiment to propose that What: Used the gold foil experiment to propose that

most of the mass of the atom was concentrated at the most of the mass of the atom was concentrated at the atom’s center (the nucleus).atom’s center (the nucleus).

Section 1: “The Development of Section 1: “The Development of the Atomic Theory”the Atomic Theory”

Rutherford’s model Rutherford’s model disclaimed disclaimed Thomson’s plum-Thomson’s plum-pudding model.pudding model.

Section 1: “The Development of Section 1: “The Development of the Atomic Theory”the Atomic Theory”

Who: Niels BohrWho: Niels Bohr When: 1922When: 1922 What: Developed What: Developed

Bohr Model of the Bohr Model of the atom.atom.

Section 1: “The Development of Section 1: “The Development of the Atomic Theory”the Atomic Theory”

Who: James Who: James ChadwickChadwick

When: 1932When: 1932 What: Discovered What: Discovered

the neutron.the neutron.

Section 1: “The Development of Section 1: “The Development of the Atomic Theory”the Atomic Theory”

Quantum Mechanical Look at the AtomQuantum Mechanical Look at the Atom

Section 2: “The Structure of Section 2: “The Structure of Atoms”Atoms”

Subatomic Subatomic ParticleParticle

LocationLocation ChargeCharge MassMass

neutron(nneutron(noo) ) nucleus nucleus 0 0 1.67x101.67x10-27-27 kg (1 amu) kg (1 amu)

proton(pproton(p++) ) nucleus nucleus +1+1 1.67x101.67x10-27-27 kg (1 amu) kg (1 amu)

electron(eelectron(e--) ) electron cloud electron cloud surrounding nucleus surrounding nucleus

11 9.11 x109.11 x10-31 -31

kg kg

Subatomic Particles of an AtomSubatomic Particles of an Atom

Section 2: “The Structure of Section 2: “The Structure of Atoms”Atoms”

Electric force from the attraction between Electric force from the attraction between the positive proton and negative electron the positive proton and negative electron holds the atom together.holds the atom together.

Section 2: “The Structure of Section 2: “The Structure of Atoms”Atoms”

The overall charge electric charge of an atom is neutral The overall charge electric charge of an atom is neutral or 0. This is because the number of protons in an or 0. This is because the number of protons in an atom is equal to the number of electrons.atom is equal to the number of electrons.

This hydrogen atom has 1 proton and 1 electron (+1 + -1 = 0)This hydrogen atom has 1 proton and 1 electron (+1 + -1 = 0)

Section 2: “The Structure of Section 2: “The Structure of Atoms”Atoms”

Atomic numberAtomic number is the number of is the number of protons in the nucleus of an atom. Each protons in the nucleus of an atom. Each element has a unique number of protons.element has a unique number of protons.

Mass numberMass number of an atom is the sum of of an atom is the sum of the numbers of protons and neutrons in the numbers of protons and neutrons in the nucleus of an atom.the nucleus of an atom.

Atomic massAtomic mass is the average weighted is the average weighted mass of an element ’s naturally occurring mass of an element ’s naturally occurring differences in the number of neutrons.differences in the number of neutrons.

Section 2: “The Structure of Section 2: “The Structure of Atoms”Atoms”

Atomic Number (Z) =Atomic Number (Z) =

66 Mass Number (A) =Mass Number (A) =

1212

Section 2: “The Structure of Section 2: “The Structure of Atoms”Atoms”

Atomic Number (Z) =Atomic Number (Z) =11

Atomic Mass (A) =Atomic Mass (A) =1.00794 amu1.00794 amu

Mass Number (A) =Mass Number (A) =11

# of protons =# of protons =1 (same as Z)1 (same as Z)

# of electrons =# of electrons =1 (same as Z)1 (same as Z)

# of neutrons =# of neutrons =0 (# of n0 (# of n00 = A – Z) = A – Z)

Section 2: “The Structure of Section 2: “The Structure of Atoms”Atoms”

An An isotopeisotope is an atom that has the same number of protons as is an atom that has the same number of protons as other atoms of the same element do but that has a different other atoms of the same element do but that has a different number of neutrons (and a different atomic mass)number of neutrons (and a different atomic mass)

Because isotopes have the same number of protons and Because isotopes have the same number of protons and electrons, they generally have similar chemical properties.electrons, they generally have similar chemical properties.

Section 2: “The Structure of Section 2: “The Structure of Atoms”Atoms”

On the periodic table, On the periodic table, the atomic mass the atomic mass displayed is an average displayed is an average of the atomic masses of of the atomic masses of all of that elements all of that elements isotopes.isotopes.

It is a weighted average It is a weighted average so the mostly so the mostly commonly found commonly found isotopes have the most isotopes have the most impact on the mass.impact on the mass.

Section 2: “The Structure of Section 2: “The Structure of Atoms”Atoms”

A A molemole is the SI base unit that describes is the SI base unit that describes the amount of a substance.the amount of a substance.

Avagadro’s constantAvagadro’s constant is the number of is the number of particles in 1 mole of a substance and is particles in 1 mole of a substance and is equal to 602213670000000000000000 equal to 602213670000000000000000 or 6.022 x 10or 6.022 x 102323..

Section 2: “The Structure of Section 2: “The Structure of Atoms”Atoms”

The The molar mass molar mass is the mass in grams of 1 mol of a is the mass in grams of 1 mol of a substance.substance.

This is equal to the atomic mass of atoms measured in grams This is equal to the atomic mass of atoms measured in grams rather than amu’s.rather than amu’s.

Example: The atomic mass of magnesium is equal to 24.30 Example: The atomic mass of magnesium is equal to 24.30 amu. The molar mass of magnesium is equal to 24.30 g.amu. The molar mass of magnesium is equal to 24.30 g.

Section 3: “The Modern Atomic Section 3: “The Modern Atomic TheoryTheory

Electrons determine charge in an atom.Electrons determine charge in an atom.

Section 3: “The Modern Atomic Section 3: “The Modern Atomic TheoryTheory

Energy levelsEnergy levels are are areas where areas where electrons can exist electrons can exist around the nucleus around the nucleus of an atom.of an atom.

Section 3: “The Modern Atomic Section 3: “The Modern Atomic TheoryTheory

The more energy an The more energy an electron has the electron has the higher the energy higher the energy level they can exist level they can exist on.on.

Electrons move from Electrons move from one level to the next one level to the next by gaining or losing by gaining or losing energy.energy.

Section 3: “The Modern Atomic Section 3: “The Modern Atomic TheoryTheory

Each energy level holds a specific Each energy level holds a specific maximum number of electrons:maximum number of electrons:

11stst = 2 = 2

22ndnd = 8 = 8

33rdrd = 18 = 18

44thth = 32 = 32

Section 3: “The Modern Atomic Section 3: “The Modern Atomic TheoryTheory

Valence electronsValence electrons are electrons that are are electrons that are found in the outermost shell of an atom and found in the outermost shell of an atom and that determine the atom’s chemical properties that determine the atom’s chemical properties and reactivity.and reactivity.

The The octet ruleoctet rule says that once an atom has 8 says that once an atom has 8 valence electrons, it will no longer be reactive (with valence electrons, it will no longer be reactive (with the exception of the first energy level which only the exception of the first energy level which only needs 2).needs 2).

Section 3: “The Modern Atomic Section 3: “The Modern Atomic TheoryTheory

An An orbitalorbital is a region in an atom where is a region in an atom where there is a high probability of finding there is a high probability of finding electrons.electrons.

Niels Bohr proposed that an atom’s Niels Bohr proposed that an atom’s electrons move around an orbital in a fixed electrons move around an orbital in a fixed path like planets around the sun.path like planets around the sun.

Modern atomic theory says that rather than Modern atomic theory says that rather than moving in fixed paths, electrons move like moving in fixed paths, electrons move like waves on a vibrating string where its exact waves on a vibrating string where its exact location cannot be determined.location cannot be determined.

Section 3: “The Modern Atomic Section 3: “The Modern Atomic TheoryTheory

Section 3: “The Modern Atomic Section 3: “The Modern Atomic TheoryTheory

An “s” orbital is shaped like a sphere and can An “s” orbital is shaped like a sphere and can hold a maximum of 2 electrons.hold a maximum of 2 electrons.

Each “p” orbital is shaped like a bar bell. Each “p” orbital is shaped like a bar bell. There are 3 different types that can each hold There are 3 different types that can each hold 2 electrons. The “p” orbital, therefore, can hold 2 electrons. The “p” orbital, therefore, can hold up to 6 electrons.up to 6 electrons.

““d” and “f” orbitals are more complex. There d” and “f” orbitals are more complex. There are 5 types of “d” orbitals and 7 types of “f” are 5 types of “d” orbitals and 7 types of “f” orbitals each that hold 2 electrons each. orbitals each that hold 2 electrons each. Therefore, in total they hold 10 and 14 Therefore, in total they hold 10 and 14 electrons respectively.electrons respectively.

Section 3: “The Modern Atomic Section 3: “The Modern Atomic TheoryTheory

Section 3: “The Modern Atomic Section 3: “The Modern Atomic TheoryTheory