Chapter Chapter 44

Atomic Atomic StructureStructure

DemocritusDemocritusGreek PhilosopherGreek Philosopher

First to suggest the First to suggest the idea of atoms.idea of atoms.

Believed atoms were Believed atoms were indivisible & indivisible & indestructibleindestructible

John DaltonJohn Dalton

English chemist English chemist & school & school teacher.teacher.

Started the Started the modern idea of modern idea of the atom.the atom.

Dalton’s Atomic Dalton’s Atomic TheoryTheoryDalton’s Atomic Theory:Dalton’s Atomic Theory:

1.1. All elements are composed of tiny All elements are composed of tiny particles called atomsparticles called atoms

2.2. Atoms of the same element are identical; atoms of Atoms of the same element are identical; atoms of one element are different than other elements.one element are different than other elements.

3.3. Atoms of different elements can physically mix or Atoms of different elements can physically mix or chemically combine in whole-number ratios to chemically combine in whole-number ratios to form compounds.form compounds.

4.4. Chemical reactions occur when atoms are Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of 1 separated, joined, or rearranged. Atoms of 1 element are never changed into another element.element are never changed into another element.

Dalton’s Atomic Dalton’s Atomic TheoryTheory

AtomsAtomsAtomAtom—smallest particle —smallest particle of an element that retains of an element that retains the properties of that the properties of that element.element.

Atoms can be detected Atoms can be detected using a scanning using a scanning tunneling microscope.tunneling microscope.

The Elements: Forged in Stars

The Origin of the Elements

Sec 2: Nuclear Sec 2: Nuclear AtomAtomAtoms are now known to be divisible.Atoms are now known to be divisible.

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

ElectronsElectrons—negatively charged subatomic particles.—negatively charged subatomic particles.

Electrons were discovered by J.J. Thomson using a Electrons were discovered by J.J. Thomson using a cathode ray.cathode ray.

Negative electrons are attracted to positively charged metal plates.

NucleusNucleusNucleusNucleus—the central core of an atom —the central core of an atom composed of protons & neutrons.composed of protons & neutrons.

The nucleus was discovered by Ernest The nucleus was discovered by Ernest Rutherford using the gold foil experiment.Rutherford using the gold foil experiment.

Protons & Protons & NeutronsNeutronsProtons—positively charged subatomic Protons—positively charged subatomic

particles.particles.

Neutrons—subatomic particles with no Neutrons—subatomic particles with no charge.charge. Discovered by Chadwick 1932Discovered by Chadwick 1932 Mass of neutron is about equal to proton (1 amu)Mass of neutron is about equal to proton (1 amu)

Atoms are neutral; they have no overall Atoms are neutral; they have no overall charge.charge. Positive protons cancel out negative electronsPositive protons cancel out negative electrons

electron

neutron

proton

IsotopesIsotopesIsotopesIsotopes—Atoms that have the same —Atoms that have the same number of protons, but different numbers number of protons, but different numbers of neutrons.of neutrons.

Atomic NumberAtomic Number

Atomic Number—the number of protons Atomic Number—the number of protons in an atom of an element.in an atom of an element.

Every element has a different number of Every element has a different number of protons.protons.

Mass NumberMass NumberMass numberMass number—the total number of protons —the total number of protons and neutrons in an atomand neutrons in an atom Mass # = protons + neutronsMass # = protons + neutrons Example: a helium atom has 2 protons and 2 Example: a helium atom has 2 protons and 2

neutrons. What is the mass number?neutrons. What is the mass number? 44 # of neutrons = mass # – atomic ## of neutrons = mass # – atomic #

Shorthand notation:Shorthand notation:

You can use the mass number to name specific atoms. Example: Helium-4

Sec. 3: Atomic Sec. 3: Atomic MassMass

The mass of a proton or neutron is The mass of a proton or neutron is 1.67 x 101.67 x 10-24-24 g. g.

The mass of an electron is 9.11 x 10The mass of an electron is 9.11 x 10-28-28 g. g. This is negligible in comparison.This is negligible in comparison.

Atomic mass unit (amu)Atomic mass unit (amu)—the 1/12 the —the 1/12 the mass of a Carbon-12 atom.mass of a Carbon-12 atom. The approx. mass of a proton or neutron.The approx. mass of a proton or neutron.

Atomic MassAtomic MassAtomic massAtomic mass—a weighted average mass —a weighted average mass of the atoms in a naturally occurring of the atoms in a naturally occurring sample of the element.sample of the element.

The atomic mass is usually closest to the The atomic mass is usually closest to the most abundant isotope of that element.most abundant isotope of that element.

Atomic MassAtomic MassTo calculate atomic mass, you need to knowTo calculate atomic mass, you need to know

1.1. The mass of each isotopeThe mass of each isotope2.2. The natural abundance of each isotope. (in The natural abundance of each isotope. (in

decimal form)decimal form)

Atomic mass of each isotope Atomic mass of each isotope x x its abundanceits abundance then add the results.then add the results.ExampleExample: Element B has 2 isotopes. One : Element B has 2 isotopes. One isotope has a mass of 10.012 amu with an isotope has a mass of 10.012 amu with an abundance of 19.92%. The other isotope has abundance of 19.92%. The other isotope has a mass of 11.009 amu with an abundance of a mass of 11.009 amu with an abundance of 80.09%. What is the atomic mass?80.09%. What is the atomic mass?

Calculating Atomic Calculating Atomic MassMass

10.012 amu x 0.1991 = 1.993 amu10.012 amu x 0.1991 = 1.993 amu

11.009 amu x 0.8009 = 11.009 amu x 0.8009 = 8.817 amu8.817 amu

atomic mass = 10.810 amuatomic mass = 10.810 amu

Done with

Section 3

Sec. 4 The Sec. 4 The Periodic TablePeriodic TableDevelopment of the Periodic Table:Development of the Periodic Table:

About 70 elements were discovered before the About 70 elements were discovered before the 1880s1880s

Dmitri Mendeleev first listed elements in a Dmitri Mendeleev first listed elements in a systematic, organized way.systematic, organized way.

He arranged atoms by their properties and in order He arranged atoms by their properties and in order of atomic mass.of atomic mass.

Mendeleev constructed the first periodic table.Mendeleev constructed the first periodic table. He left blank places for unknown elements.He left blank places for unknown elements. Henry Moseley determined atomic # and arranged Henry Moseley determined atomic # and arranged

elements by this instead of atomic mass. elements by this instead of atomic mass.

The Modern The Modern Periodic TablePeriodic TableEach element is represented by its symbol Each element is represented by its symbol

and atomic number placed in a squareand atomic number placed in a square

The horizontal arrangement of elements The horizontal arrangement of elements are called are called periods.periods.

Periodic LawPeriodic Law—when the elements are —when the elements are arranged in order of increasing atomic arranged in order of increasing atomic number, there is a repeated pattern of number, there is a repeated pattern of physical and chemical properties.physical and chemical properties.

The Modern The Modern Periodic TablePeriodic Table

GroupGroup—a vertical arrangement of atoms.—a vertical arrangement of atoms.

The elements in any group have similar The elements in any group have similar chemical and physical properties.chemical and physical properties.

Each group is identified by a number and Each group is identified by a number and letter A or B.letter A or B.

The Modern The Modern Periodic TablePeriodic Table

Group A elements are known as Group A elements are known as representative elementsrepresentative elements..

Representative elements are broken into 3 Representative elements are broken into 3 classes.classes. Metals—high electrical conductivity and lusterMetals—high electrical conductivity and luster Alkali metals—Group 1AAlkali metals—Group 1A Alkaline Earth Metals—Group 2A elementsAlkaline Earth Metals—Group 2A elements

Most non-representative elements are also Most non-representative elements are also metalsmetals

The Modern The Modern Periodic TablePeriodic Table

Nonmetals—occupy upper right corner of Nonmetals—occupy upper right corner of the periodic table.the periodic table. Nonlustrous and poor conductors of electricity.Nonlustrous and poor conductors of electricity. Some are gases, some are solidsSome are gases, some are solids

2 nonmetal groups have special names2 nonmetal groups have special names Halogens—group 7A (ex. chlorine & bromine)Halogens—group 7A (ex. chlorine & bromine) Noble gases—group 8A (or group 0)Noble gases—group 8A (or group 0)

Inert gases—they do not undergo chemical Inert gases—they do not undergo chemical reactionsreactions

Ex. Neon gas is used in neon lights.Ex. Neon gas is used in neon lights.

The Modern The Modern Periodic TablePeriodic Table

MetalloidsMetalloids—elements with properties that —elements with properties that are intermediate between metals and are intermediate between metals and nonmetals.nonmetals.

A heavy line divides metals from A heavy line divides metals from nonmetals.nonmetals.

Most elements that border this line are Most elements that border this line are metalloids.metalloids.