Atoms and Elements Goals: 1.Describe atomic structure and define atomic number and mass number. 2.Understand the nature of isotopes and calculate atomic.

Atoms and ElementsAtoms and Elements

Goals:

1. Describe atomic structure and define atomic number and mass number.

2. Understand the nature of isotopes and calculate atomic weight from the isotopic masses and abundances.

3. Explain the concept of the mole and use molar mass in calculations.

4. Know the terminology of the periodic table.

The Atomic StructureThe Atomic StructureExperimental basisExperimental basis

• One of the pieces of evidence for the fact One of the pieces of evidence for the fact that atoms are made of smaller particles that atoms are made of smaller particles

came from the work of came from the work of Marie CurieMarie Curie (1876-1934). (1876-1934).

• She discovered She discovered ______________________, the , the spontaneous disintegration of some spontaneous disintegration of some elements into smaller pieces.elements into smaller pieces. - Rays emitted by polonium and radium – radioactive atoms disintegrate and emit rays: alpha (a), beta (b), gamma (g).

**Contradicted Dalton’s postulate: “atoms are indivisible”.

Experiment: RadiationExperiment: Radiation

• Three rays:

Experiment: Cathode-Ray Experiment: Cathode-Ray TubesTubes

• Electrons:

Same charge-to-mass ratio detected for different Same charge-to-mass ratio detected for different elements: electrons are present in all atoms.elements: electrons are present in all atoms.

Millikan (charge of the electron), Goldstein (positive Millikan (charge of the electron), Goldstein (positive ions).ions).

Rutherford’s Gold Foil ExperimentRutherford’s Gold Foil Experiment

• Nucleus and the protons:

(+)

Chadwick (neutrons).Chadwick (neutrons).

The Atomic StructureThe Atomic Structure• J.J. Thomson and E. Rutherford (England

~1900) established a model of the atom – the basis of modern atomic theory.

• Three subatomic particles:– Electrically positive protons– Mass = 1.672622 x 10Mass = 1.672622 x 10-24-24 g g– Relative mass = 1.007 atomic mass units (u)Relative mass = 1.007 atomic mass units (u)

– Electrically neutral neutrons– Relative mass = 1.009 uRelative mass = 1.009 u

– Electrically negative electrons– Relative mass = 0.0005 uRelative mass = 0.0005 u

– Which particle is heavier, which particle is Which particle is heavier, which particle is lighter?lighter?

____________ _______________

Atom CompositionAtom Composition

• The atom is mostly empty space.

• protons and neutrons in the nucleus.

• the number of electrons is equal to the number of protons.

• electrons in space around the nucleus.

• extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water.

How big is an atom?How big is an atom?

• The radius of the typical atom is between 30 and 300 pm (3 x 10-11 m to 3 x 10-10 m). The radius of the nucleus is about 0.001 pm.

• If an atom were a macroscopic object, about the size of a football stadium, what would be the radius of the nucleus?– __________________

What is Atomic Number?What is Atomic Number?

Atomic number (Z) is the number of _____________ in the nucleus of an element.

1313

AlAl

26.98126.981

Atomic numberAtomic number

Atom symbolAtom symbol

Atomic weightAtomic weight

• All atoms of the same element have the same All atoms of the same element have the same number of __________ in the nucleus.number of __________ in the nucleus.

What is Mass Number?What is Mass Number?

The mass number (A) is the number of ____________ plus the number of ____________ in the nucleus of an element.

C atomC atom with 6 protons and 6 neutrons is with 6 protons and 6 neutrons is the mass standard = 12 atomic mass the mass standard = 12 atomic mass units (u)units (u)

1 u = 1.661 x 101 u = 1.661 x 10-24-24 g g

Mass NumberMass Number (A) = # protons + # (A) = # protons + # neutronsneutrons CC1212

66XXAAZZ

What is the mass number of an iron What is the mass number of an iron atom with 30 neutrons?atom with 30 neutrons?

• The periodic table gives the atomic number for iron:

• Why the periodic table gives a WEIGHT of = 55.845 ?

2626

FeFe

Atomic numberAtomic number

Atom symbolAtom symbol

Atomic weightAtomic weight

Percent AbundancePercent Abundance

50%/50% mixture50%/50% mixture 90%/10% mixture90%/10% mixture

What are isotopes? How do What are isotopes? How do they affect atomic weight?they affect atomic weight?

• Isotopes:Isotopes: ___________________________ __________________________________.

• Because of the presence of atoms, the Because of the presence of atoms, the mass of a collection of atoms is an mass of a collection of atoms is an averageaverage of values.of values.

Average mass = Average mass = ATOMIC WEIGHTATOMIC WEIGHT

Boron is 19.9% 10B and 80.1% 11B. That is, 11B is 80.1 percent abundant on earth.

• What is the atomic weight of boron? _________________

How many isotopes for H?How many isotopes for H?

1H

1H

1H1 proton and 2 neutrons, tritium(radioactive)

1 proton and 1 neutron, deuterium

1 proton and 0 neutrons, protium

1

2

3

Gallium has two isotopes: Gallium has two isotopes: 6969Ga and Ga and 7171Ga.Ga.How many protons and neutrons are in the nuclei of How many protons and neutrons are in the nuclei of each of these isotopes? If the abundance of each of these isotopes? If the abundance of 6969Ga is Ga is

60.1%, what is the abundance of 60.1%, what is the abundance of 7171Ga?Ga?

Students should become familiar with the use of atomic number and mass

number,especially in isotopes calculations.

How are the masses of isotopes How are the masses of isotopes and their % abundances and their % abundances

determined?determined?• They are experimentally determined by

using a ___________________________.

By changing the magnetic field, a beam By changing the magnetic field, a beam of charged particles of different mass of charged particles of different mass can be focused on the detector, and a can be focused on the detector, and a spectrum of masses is observed.spectrum of masses is observed.

Copper exists as two isotopes: Copper exists as two isotopes: 6363Cu (62.9298 u) and Cu (62.9298 u) and 6565Cu (64.9278 u). What is the approximate Cu (64.9278 u). What is the approximate

percentage of percentage of 6363Cu in samples of this element?Cu in samples of this element?

Congratulations! You discovered a Congratulations! You discovered a new element…new element…

you name wyzzlebium (Wz). The average atomic mass of Wz was found to be 303.001 amu and its atomic number is 120.

A) If the masses of the two isotopes of Wz are 300.9326 amu and 303.9303 amu, what is the relative abundance of each isotope?

Congratulations! You discover a Congratulations! You discover a new element…new element…

B) What are the isotopic notations of the two isotopes? (e.g. W).

C) How many neutrons are in one atom of the more abundant isotope?

AAZZ

What is Atomic Weight?What is Atomic Weight?

• This tells us the mass of one atom of an element relative to one atom of another element.

• OR — the mass of 1000 atoms of one element relative to 1000 atoms of another.

• Example: an O atom is approximately 1.333 times heavier than an C atom.

• Define one element as the standard against which all others are measured

• Standard = carbon

Counting atomsCounting atoms

• In chemical reactions, how can we predict the amount of product given the mass of reactant?

Mg burns in air (OMg burns in air (O22) to ) to produce white magnesium produce white magnesium oxide, MgO. oxide, MgO.

The Periodic TableThe Periodic Table

• Dmitri Mendeleev developed the modern Dmitri Mendeleev developed the modern periodic table. Argued that element periodic table. Argued that element properties are properties are periodic functions of their atomic weights.

• We We now knownow know that element properties are that element properties are periodic functions of their periodic functions of their __________ __________ (G. J. Moseley) . – Law of Chemical Periodicity

Students should become familiar with the organization of elements in the periodic

table.

The Periodic TableThe Periodic Table

Period

Family orGroup

ElementsElements

• Metals– Solid (except for mercury)– Conduct electricity– Ductile (can be drawn into wires)– Malleable (can be rolled into sheets)– Alloys (solutions of one metal into another metal)

• Metalloids (semimetals)– Physical characteristics of metals, but chemical

characteristics of nonmetals.

• Nonmetals– Do not conduct electricity (except from C – graphite)

HydrogenHydrogen

• Non-metal.• Most abundant element in

the universe.• Lightest element.

Group IA: Alkali MetalsGroup IA: Alkali Metals

• React with water to give alkaline solutions.

• Found in nature only combined in compounds.

Group IIA: Alkaline Earth Group IIA: Alkaline Earth MetalsMetals

• React with water to give alkaline solutions (except Be).

• Found in nature only combined in compounds.

Group IIIAGroup IIIA

• All metals, but boron is a metalloid.• Aluminum is the most abundant metal in the

earth’s crust by mass (8.2%).

Al resists corrosion (in HNO3).

Gallium can be a liquid at room temp.

Cu Al

Group IVAGroup IVA

• C has large biological importance.• Nonmetal: C, Metalloids: Si, Ge, Metals: Sn, Pb.• All form analogous compounds such as their oxides:

CO2, SiO2, GeO2, SnO2, PbO2.

Diamond

Quartz, SiO2

What are allotropes?What are allotropes?

• Characteristic of the chemistry of nonmetals.• Allotropes:Allotropes: _________________________

_______________________ each having its own properties.

• C: graphite, diamond, buckminsterfullerene.

The periodic tableThe periodic table

PracticePractice

• Decide which represents more mass:a)10 atoms of Fe or 10 atoms of K

b) 9 g of Na or 0.5 mol of Na

Group VAGroup VA

White and red P

• N2: makes up about ______ of earth’s atmosphere.

• N and P have biological importance.

• P has several allotropes.

• Nonmetals: N2 and P, Metalloids: As and Sb, Metal: Bi.

• Analogous oxides: N2O5, P2O5, As2O5.

Group VIAGroup VIA

• O2: makes up ______of earth’s atmosphere.

• S, Se, Te are the chalcogens (present in cupper ores).

• O2 has an allotrope: O3 (ozone).

• Nonmetals: O2, S and Se, Metalloids: Te, Metal: Po (radioactive).

• Analogous oxides: SO2, SeO2, TeO2.

Group VIIA: HalogensGroup VIIA: Halogens

• All nonmetals, named the halogens (salt forming, they react violently with metals of group IA.

• All exist as diatomic molecules.

• F2 and Cl2 are gases. Br2 is a liquid. I2 is a solid.

Group VIIIA: Noble GasesGroup VIIIA: Noble Gases

• The least reactive elements (called inert gases). • Helium is the second most abundant element in the

universe. But non is abundant on earth or earth’s atmosphere (also called rare gases).

• All are gases.

The Transition ElementsThe Transition Elements

LanthanidesActinides

The Transition ElementsThe Transition Elements

• Most occur naturally in compounds. Ag, Au, and Pt are much less reactive and can be found in nature as pure elements.

• Some are of biological importance: Fe, Zn, Cu, Co.

Essential ElementsEssential Elements

• Found in hemoglobin (Fe), vitamin B12 (Co).

PracticePractice• Element in the 2th period, group 3A• Alkali metal in the 4th period• Metalloid in group 6A• Noble gas in 3th period

Units for countingUnits for counting

1 dozen = 12 objects Eggs are measured by the dozen

1 ream = 500 objectsPaper is measured by the ream, 500

sheets

Counting atomsCounting atoms

Chemistry is a quantitative science—we need a “counting unit.”

MOLE

Definition:Definition: 1 MOLE is the amount of substance that contains as many particles (atoms, molecules) as there are in __________________.

How many Particles in one How many Particles in one Mole?Mole?

• Amedeo Avogadro (1776-1856).

• There is Avogadro’s number of particles in a mole of any substance.

6.02214199 x 1023

1 mole = 6.022 x 1023 items

What is Molar Mass?What is Molar Mass?

1 mol of 12C = 12.00 g of C = 6.022 x 1023 atoms of C

12.00 g of 12C is its MOLAR MASS

Taking into account all of the isotopes of C, the molar mass of C is 12.011 g/mol.

One Mole AmountsOne Mole Amounts

SummarySummary

• The atomic mass expressed in grams is the molar mass of an element. It is different for each element.

1 molar mass = atomic mass of an element in grams

• One mole of any element contains Avogadro’s number of atoms.

1 mol of atoms = 6.022 x 1023 atoms

You can use these relationships to make conversions between number of atoms, mass, and moles.

MassMass Moles Moles ConversionConversion

It is essential to convert from moles to mass and from mass to moles.

MolesMoles xxgramsgrams

1 mol1 mol

molar massmolar mass

= grams= grams GramsGrams xx1 mol1 mol

gramsgrams

1/molar mass1/molar mass

= moles= moles

What amount of Mg in moles is represented by 0.200 g? How many atoms?

Mg has a molar mass of 24.3050 g/mol.

12Mg

24.3050

Atomic numberAtom symbol

Atomic weight

Students should become familiar with calculations using molar mass and

avogadro’s number.

RememberRemember

• Go over all the contents of your textbook.

• Practice with examples and with problems at the end of the chapter.

• Practice with OWL tutor.• Practice with the quiz on CD of

Chemistry Now.• Work on your assignment for Chapter

2.