Chapter 4Chapter 4

Atoms and the Periodic TableAtoms and the Periodic Table

Atomic StructureAtomic Structure

What are Atoms?What are Atoms?Democritus (Greece, 400BC) named the Democritus (Greece, 400BC) named the smallest bit of matter unable to be divided the smallest bit of matter unable to be divided the ATOMATOMJohn Dalton (1808) proposed the Atomic (1808) proposed the Atomic Theory:Theory: Atoms are the building blocks of matterAtoms are the building blocks of matter Atoms of given elements are exactly the sameAtoms of given elements are exactly the same Atoms of different elements are differentAtoms of different elements are different

Examples:Examples:

Atomic CompositionProtons: Protons: In the nucleusIn the nucleus Positive chargePositive charge Mass of about 1 amu (atomic mass unit)Mass of about 1 amu (atomic mass unit)

Electron:: Outside the nucleusOutside the nucleus Negative chargeNegative charge Mass is about 0 amuMass is about 0 amu

Neutron:Neutron: In the nucleusIn the nucleus No chargeNo charge Mass is about 1 amuMass is about 1 amu

Atom ModelsAtom Models

Bohr Model (1913): electrons move in set (1913): electrons move in set paths around the nucleus much like the paths around the nucleus much like the planets in the planets in the solar system

An Electron has a certain energy An Electron has a certain energy determined by its pathdetermined by its path

Electrons can be in only one energy level Electrons can be in only one energy level but can move to higher and lower energy but can move to higher and lower energy levels by gaining or losing energylevels by gaining or losing energy

Atom Models cont.Atom Models cont.Many atomic models were proposed until the widely Many atomic models were proposed until the widely

accepted wave model of today accepted wave model of today Electrons do not have definite paths but behave Electrons do not have definite paths but behave more like waves on vibrating strings rather than more like waves on vibrating strings rather than particlesparticlesAn electron’s exact location cannot be determinedAn electron’s exact location cannot be determinedElectrons exist in orbitals within energy levelsElectrons exist in orbitals within energy levelsElectrons in the outermost energy levels are called Electrons in the outermost energy levels are called valence electrons – there are between 1 and 8valence electrons – there are between 1 and 8

Sect. 2:Touring the Sect. 2:Touring the Periodic Table

OrganizationOrganizationSimilar elements are grouped togetherSimilar elements are grouped togetherPeriodic law states that similar properties occur Periodic law states that similar properties occur in patternsin patternsElements are represented by Elements are represented by symbolssymbols (Gold – (Gold – Au, Nitrogen – N)Au, Nitrogen – N)Elements are in order of Elements are in order of atomic numberatomic number (number of protons in the nucleus)(number of protons in the nucleus)Periods – rows (across) – rows (across)Groups – columns (up and down) – columns (up and down)

What do the numbers mean?What do the numbers mean?

Atomic numberAtomic number: : Each element has its own atomic numberEach element has its own atomic number number of protons in the nucleusnumber of protons in the nucleus For a neutral atom, also the number of electronsFor a neutral atom, also the number of electrons

Mass numberMass number:: Round the Round the atomic massatomic mass Mass of nucleus=protons +neutronsMass of nucleus=protons +neutrons

Isotope: : different ‘versions’ of an element that contains a different different ‘versions’ of an element that contains a different

number of neutrons number of neutrons an average of all these occurring isotopes in nature an average of all these occurring isotopes in nature

results in the atomic mass listed on the periodic tableresults in the atomic mass listed on the periodic table

How many subatomic particles in How many subatomic particles in an atom?an atom?

Protons: the atomic numberProtons: the atomic number

Electrons: the atomic numberElectrons: the atomic number

Neutrons: mass number – atomic numberNeutrons: mass number – atomic number

Examples: CarbonCarbon HydrogenHydrogen PotassiumPotassium

Section 3: Element FamiliesSection 3: Element FamiliesMetals: left of staircase, shiny, ductile, malleable, and Metals: left of staircase, shiny, ductile, malleable, and

good conductors of heat and electricitygood conductors of heat and electricityAlkali Metals::

Group 1 (1A), Group 1 (1A), one valence electronone valence electron Soft and shinySoft and shiny React with waterReact with water

Alkaline Earth Metals:Alkaline Earth Metals: Group 2 (2A), 2 valence electronsGroup 2 (2A), 2 valence electrons

Transition Metals:Transition Metals: Groups 3-12 (IIIB-IIB), Groups 3-12 (IIIB-IIB), 1 or 2 valence electrons1 or 2 valence electrons Some of these metals can form more than one cationSome of these metals can form more than one cation

Families (cont)Families (cont) Nonmetals: right side of the tableNonmetals: right side of the table

Halogens:Halogens: Group 17 (VIIA), Group 17 (VIIA), 7 valence electrons7 valence electrons Highly reactiveHighly reactive Form halides (salts) with metalsForm halides (salts) with metals

Noble gasesNoble gases Group 18(VIIIA), 8 valence electrons (He 2)Group 18(VIIIA), 8 valence electrons (He 2) Inert, nonreactiveInert, nonreactive

Metalloids:Metalloids: Located along the staircaseLocated along the staircase Have characteristics of metals and nonmetalsHave characteristics of metals and nonmetals NOT aluminumNOT aluminum

Chapter 4 section 4:Chapter 4 section 4:What is a Mole!?What is a Mole!?

Counting: dozen, ream, gross, moleCounting: dozen, ream, gross, mole

Mole = 6.022 x 10Mole = 6.022 x 102323 particles particles

In chemistry, one mole = 6.022 x 10In chemistry, one mole = 6.022 x 102323 atoms atoms

Conversion factor = 1Conversion factor = 1 1kg/ 1000g, 365 days/ 1 year, 365 days/8760hours, 1kg/ 1000g, 365 days/ 1 year, 365 days/8760hours,

1 mol Mg/24.3050 g or 24.3050 g/1 mol1 mol Mg/24.3050 g or 24.3050 g/1 mol

Example of unit conversions:Example of unit conversions:How old am I, in seconds?How old am I, in seconds?

Start with given information.Start with given information.

End with correct units.End with correct units.

Remember the identity element of algebra.Remember the identity element of algebra.

Amount to Mass:Amount to Mass:

1.1. Write the given over the number oneWrite the given over the number one

50 moles of iron/150 moles of iron/1

2. Multiply by the molar mass of the 2. Multiply by the molar mass of the element: ---g/1 molelement: ---g/1 mol

(50 moles of iron/1) x (55.845 g of Fe/ 1 mol (50 moles of iron/1) x (55.845 g of Fe/ 1 mol of iron)of iron)

3. Check your units: grams3. Check your units: grams

Mass to amount:Mass to amount:

1.1. Write the given mass over the number Write the given mass over the number one: 98 g of carbon/1one: 98 g of carbon/1

2.2. Multiply by the molar mass: 1 mol/---gMultiply by the molar mass: 1 mol/---g

(98 g of carbon/1) x (1mol carbon/12 g of (98 g of carbon/1) x (1mol carbon/12 g of carbon)carbon)

3. Check your units: moles3. Check your units: moles