Elements, Atoms, and

Isotopes***Green indicates test items***

The Language of The Language of ChemistryChemistryThe Language of The Language of ChemistryChemistry

• CHEMICAL ELEMENTSCHEMICAL ELEMENTS - - – pure substances that cannot be decomposed by pure substances that cannot be decomposed by

ordinary means to other substances.ordinary means to other substances.

SodiumBromine

Aluminum

The Language of The Language of ChemistryChemistryThe Language of The Language of ChemistryChemistry

• The elements, The elements, their names, and their names, and symbols are given symbols are given on theon the PERIODIC PERIODIC TABLETABLE

• How many How many elements are elements are there?there?

An atom consists of a An atom consists of a

• nucleus nucleus

– (of protons and neutrons) (of protons and neutrons)

• electrons in space around the electrons in space around the nucleus.nucleus.

The The AtomAtom

NucleusNucleus

Electron cloudElectron cloud

Copper Copper atoms on atoms on silica silica surface.surface.

• An An _____ _____ is the smallest particle of is the smallest particle of an element that has the chemical an element that has the chemical properties of the element.properties of the element.

Distance across = 1.8 nanometer (1.8 x 10-9 m)

Subatomic ParticlesSubatomic Particles

• Quarks

– component of component of protons & protons & neutronsneutrons

– 6 types6 types

– 3 quarks = 3 quarks = 1 proton or 1 proton or 1 neutron1 neutron

He

The red compound is The red compound is composed ofcomposed of• • nickel (Ni) (silver)nickel (Ni) (silver)• • carbon (C) (black)carbon (C) (black)• hydrogen (H) (white)• hydrogen (H) (white) • • oxygen (O) (red)oxygen (O) (red)• • nitrogen (N) (blue)nitrogen (N) (blue)

The red compound is The red compound is composed ofcomposed of• • nickel (Ni) (silver)nickel (Ni) (silver)• • carbon (C) (black)carbon (C) (black)• hydrogen (H) (white)• hydrogen (H) (white) • • oxygen (O) (red)oxygen (O) (red)• • nitrogen (N) (blue)nitrogen (N) (blue)

CHEMICAL COMPOUNDSCHEMICAL COMPOUNDS are composed of atoms and so can are composed of atoms and so can be decomposed to those atoms.be decomposed to those atoms.

Compounds

– composed of 2 or more elements in a fixed ratio

– properties differ from those of individual elements

– EX: table salt (NaCl)

A A MOLECULEMOLECULE is the smallest unit of is the smallest unit of a compound that retains the chemical a compound that retains the chemical characteristics of the compound.characteristics of the compound.

Composition of molecules is given by aComposition of molecules is given by a

MOLECULAR FORMULAMOLECULAR FORMULA

HH22OO CC88HH1010NN44OO22 - caffeine - caffeine

ATOM ATOM COMPOSITIONCOMPOSITION

•protons and neutrons in protons and neutrons in the nucleus.the nucleus.

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

•electrons in space around the nucleus.electrons in space around the nucleus.

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

The atom is mostlyThe atom is mostlyempty spaceempty space

ATOMIC COMPOSITIONATOMIC COMPOSITION• Protons (pProtons (p++))

– positive electrical chargepositive electrical charge

– mass = 1.672623 x 10mass = 1.672623 x 10-24-24 g g

– relative mass = 1.007 atomic relative mass = 1.007 atomic mass units mass units (amu) (amu) but we can round to 1but we can round to 1

• Electrons (eElectrons (e--))– negative electrical chargenegative electrical charge

– relative mass = 0.0005 amu relative mass = 0.0005 amu but we can round to 0but we can round to 0

• Neutrons (nNeutrons (noo))– no electrical chargeno electrical charge

– mass = 1.009 amu mass = 1.009 amu but we can round to 1but we can round to 1

Atomic Number, ZAtomic Number, Z

All atoms of the same element All atoms of the same element have the same number of have the same number of protons in the nucleusprotons in the nucleus, , ZZ

1313

AlAl

26.98126.981

Atomic numberAtomic number

Atom symbolAtom symbol

AVERAGE Atomic MassAVERAGE Atomic Mass

Mass Number, AMass Number, A• C atom with 6 protons and 6 neutrons C atom with 6 protons and 6 neutrons

is the mass standard is the mass standard • = 12 atomic mass units= 12 atomic mass units• Mass Number Mass Number (A)(A)

= # protons + # neutrons= # protons + # neutrons• NOT on the periodic table…(it is the NOT on the periodic table…(it is the

AVERAGE atomic mass on the table)AVERAGE atomic mass on the table)• A boron atom can have A boron atom can have

A = 5 p + 5 n = 10 amuA = 5 p + 5 n = 10 amu

A

Z

10

5B

A

Z

10

5B

IsotopesIsotopes

• Atoms of the same element Atoms of the same element (same Z) (same Z) but different mass number but different mass number (A).(A).

• Boron-10 (Boron-10 (1010B) has 5 p and 5 nB) has 5 p and 5 n

• Boron-11 (Boron-11 (1111B) has 5 p and 6 nB) has 5 p and 6 n

10B

11B

Figure 3.10: Two isotopes of sodium.

Isotopes Isotopes & Their & Their

UsesUsesBone scans with Bone scans with radioactive radioactive technetium-99. technetium-99.

Isotopes & Their Isotopes & Their UsesUses

The The tritiumtritium content of ground water is content of ground water is used to discover the source of the water, used to discover the source of the water, for example, in municipal water or the for example, in municipal water or the source of the steam from a volcano. source of the steam from a volcano.

Atomic Symbols

Show the name of the element, a hyphen, and

the mass number in hyphen notation

sodium-23

Show the mass number and atomic number

in nuclear symbol formmass number 23 Na

atomic number 11

Isotopes?

Which of the following represent isotopes of the same element? Which element?

234 X 234

X235

X238

X

92 93 92 92

Counting Protons, Neutrons, and Electrons

• Protons: Atomic Number Protons: Atomic Number (from periodic table)• Neutrons: Mass Number minus the number of protons Neutrons: Mass Number minus the number of protons

(mass number is protons and neutrons because the mass of electrons is negligible)

• Electrons: – If it’s an atom, the protons and electrons must be

the SAME so that it is has a net charge of zero (equal numbers of + and -)

– If it does NOT have an equal number of electrons, it is not an atom, it is an ION. For each negative charge, add an extra electron. For each positive charge, subtract an electron (Don’t add a proton!!! That changes the element!)

Learning Check – Counting

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C 14C 6 6 6

#p+ _______ _______ _______

#no _______ _______ _______

#e- _______ _______ _______

Answers

12C 13C 14C 6 6 6

#p+ 6 6 6

#no 6 7 8

#e- 6 6 6

Learning Check

An atom has 14 protons and 20 neutrons.A. Its atomic number is

1) 14 2) 16 3) 34

B. Its mass number is1) 14 2) 16 3) 34

C. The element is1) Si 2) Ca 3) Se

D. Another isotope of this element is

1) 34X 2) 34X 3) 36X 16 14 14

AVERAGE AVERAGE ATOMIC ATOMIC MASSMASS

• Because of the existence of isotopes, the Because of the existence of isotopes, the mass of a collection of atoms has an average mass of a collection of atoms has an average value.value.

• Boron is 20% Boron is 20% 1010B and 80% B and 80% 1111B. That is, B. That is, 1111B is B is 80 percent abundant on earth. 80 percent abundant on earth.

• For boron atomic weightFor boron atomic weight

= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu

10B

11B

Isotopes & Average Atomic Isotopes & Average Atomic MassMass

• Because of the existence of isotopes, the mass Because of the existence of isotopes, the mass of a collection of atoms has an average value.of a collection of atoms has an average value.

• 66Li = 7.5% abundant and Li = 7.5% abundant and 77Li = 92.5%Li = 92.5%

–Avg. Atomic mass of Li = ______________Avg. Atomic mass of Li = ______________

• 2828Si = 92.23%, Si = 92.23%, 2929Si = 4.67%, Si = 4.67%, 3030Si = 3.10%Si = 3.10%

–Avg. Atomic mass of Si = ______________Avg. Atomic mass of Si = ______________