CHAPTER 2chemphys.armstrong.edu/nivens/GeneralChemistry/CHapter2kotz.pdf · CHAPTER 2 Atoms and Elements 2 ... second letter lower case –C, Ca, Co –CO is not an element. 6. 7

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CHAPTER 2

Atoms and Elements

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Atoms• Dalton’s Atomic Theory - 1808

1. -Element is composed of small, indivisible particles called atoms.

2. -Atoms of an element have identical properties that differ from those of other elements.

3. -Atoms cannot be created, destroyed, or transformed -Compounds are formed when atoms of different elements combine in whole-number ratios.

4. -Atom ratios are constant in a given compound.

5. Chemical Reactions rearrange and recombine atoms but do not destroy them.

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Structure of the Atom

1. The atom is mostly empty space.

2. It contains a very small, dense center called the nucleus.

3. Nearly all of the atom’s mass is in the nucleus.

4. The nuclear diameter is 1/10,000 to 1/100,000 times less than atom’s radius.

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Fundamental Particles

Partic le M ass (amu) Charge

E lectron (e-) 0 .00054858 -1

P roton (p ,p+) 1 .0073 +1

Neutron (n ,n0) 1 .0087 0

• Three fundamental particles make up atoms. The

following table lists these particles together with

their masses and their charges.

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Elements

• Elements– substances that cannot be decomposed into simpler substances via chemical reactions

• Elemental symbols– found on periodic chart

– First letter capital, second letter lower case

– C, Ca, Co

– CO is not an element.

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Atomic Number• The atomic number is equal to the number of protons in the nucleus.– Sometimes given the symbol Z.

– Numbered consecutively on the periodic table

• The atomic number determines the element .– The elements differ from each other by the number of protons in the nucleus.

– The number of electrons in a neutral atom is also equal to the atomic number.

– For charged species there are more electrons if it is negative and less electrons if it is positive

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Mass Number and Isotopes• Mass number is given the symbol A.

• A is the sum of the number of protons and neutrons.

– Z = proton number N = neutron number

– A = Z + N

• A common symbolism used to show mass and proton numbers is

AuCa, C, example for E 197

79

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20

12

6

A

Z

?Cu, N, 18

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63

?

14

?

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Mass Number and Isotopes• How many protons and neutrons are in the following?

U

U

O

O

236

92

238

92

18

8

16

8

−

−

+

+

232

16

82

35

240

20

23

11

S

Br

Ca

Na

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Mass Number and Isotopes

Give the number of protons, neutrons and electrons and the correct element symbol

?

?

?

15

7

200

79

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12

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Isotopes

• Isotopes are atoms of the same element but with different numbers of neutrons.– Isotopes have different masses and A values but are the same element.

• One example of an isotopic series is the hydrogen isotopes.1H or protium is the most common hydrogen isotope.• one proton and no neutrons

2H or deuterium is the second most abundant hydrogen isotope.• one proton and one neutron

3H or tritium is a radioactive hydrogen isotope. • one proton and two neutrons

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The Atomic Weight Scale and Atomic

Weights

• The atomic weight of an element is the weighted average of the masses of its stable isotopes

• Example: Naturally occurring Cu consists of 2 isotopes. It is 69.1% 63Cu with a mass of 62.9 amu, and 30.9% 65Cu, which has a mass of 64.9 amu. Calculate the atomic weight of Cu to one decimal place.

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The Atomic Weight Scale and Atomic

Weights

copperfor amu 63.5 weight atomic

amu) .9(0.309)(64 amu) .9(0.691)(62 weight atomic

isotopeCu isotopeCu 6563

=

+=444 3444 21444 3444 21

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Atomic Mass• The atomic mass of an element on the periodic table is the

weighted average of the masses of its stable isotopes

– For example H = 1.008 amu

– Calcium = 40.078 amu

We will use these masses later for chemical calculations

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Atomic Weights

• Weighted average of the masses of the isotopes

• Tells us the atomic masses of every known element.

• How do we know what the values of these numbers are?

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The Mole

• A number of atoms, ions, or molecules that is large enough to see and handle.

• A mole = number of things

– Just like a dozen = 12 things

– One mole = 6.022 x 1023 things

• Avogadro’s number = 6.022 x 1023

– Symbol for Avogadro’s number is NA.

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The Mole

• Molar mass - mass in grams numerically equal to the atomic weight of the element in grams.

• H has an atomic weight of 1.00794 g

– 1.00794 g of H atoms = 6.022 x 1023 H atoms

• Mg has an atomic weight of 24.3050 g

– 24.3050 g of Mg atoms = 6.022 x 1023 Mg atoms

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The Mole

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The Mole

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The Mole

• Calculate the mass of a single Mg atom in grams to 3 significant figures.

= Mgg ?

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The Mole

• Calculate the mass of a single Mg atom, in grams, to 3 significant figures.

Mg g 104.04atoms Mg mol 1

Mgg24.30

atoms Mg 106.022

atoms Mg mol 1atom Mg 1Mg g ?

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−×=

×

×=

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The Mole

• Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.

=atoms Mg?

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The Mole

• Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.

atoms Mg102.48atoms Mgmol 1

atoms Mg106.022

Mgg 24.30

Mg mol 1 Mgg 101.00atoms Mg?

1623

6

×=

×

×= −

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The Mole

• How many atoms are contained in 1.67 moles of Mg?

=atoms Mg ?

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The Mole

• How many atoms are contained in 1.67 moles of Mg?

atoms Mg101.00

Mgmol 1

atoms Mg106.022Mg mol 1.67atoms Mg?

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23

×=

×=

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The Mole

• How many moles of Mg atoms are present in 73.4 g of Mg?

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The Mole

• Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg?

Mg mol 02.3

Mg g 24.30

atoms Mg mol 1 Mg g 4.73Mg mol ?

=

=

YOU MUST KNOWHOW TO DO THESE PROBLEMS

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The Periodic Table: Metals, Nonmetals, and Metalloids

• 1869 - Mendeleev & Meyer

– Discovered the periodic law

• The properties of the elements are periodic functions of their atomic numbers.

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• Groups or families– Vertical group of elements on periodic table

– Similar chemical and physical properties

•Period

–Horizontal group of elements on periodic table

–Transition from metals to nonmetals

•Three regions

–Metals, nonmetals and metalloids

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• Period– Horizontal group of elements on periodic table

– Transition from metals to nonmetals

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• Groups or families– Vertical group of elements on periodic table

– Similar chemical and physical properties

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• Stair step function on periodic table separates metals from nonmetals.

• Metals are to the left of stair step.– Approximately 80% of the

elements

• Nonmetals are to the right of stair step. – Approximately 20% of the

elements

• Metalloids have one side of the box on the stair step.– Properties between metals and

nonmetals

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• Periodic trends in metallic character

PeriodicChart

More MetallicMoreMetallic

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• Chemical properties of metals1. -Outer (valence) shells contain few electrons2. -Form cations by losing electrons3. -Form ionic compounds with nonmetals4. -Solid state characterized by metallic bonding

-Conductors (electricity and heat)-Malleable - hammered-Ductile – drawn-Typically solids (except mercury)

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The Periodic Table: Metals

• Group IA metals

– Alkali metals Li, Na, K, Rb, Cs, Fr

• Group IIA metals

– Alkaline earth metals Be, Mg, Ca, Sr, Ba, Ra

Group 3 – 12 – Transition

metals

Lanthanides

Actinides

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• Chemical properties of nonmetals1. -Outer shells contain four or more electrons2. -Form anions by gaining electrons (- charge)3. -Form ionic compounds with metals and covalent

compounds with other nonmetals4. -Form covalently bonded molecules; noble gases are

monatomic5. -Insulators6. Noble gasses have full shells7. Poor conductors8. Typically gasses or solids (Br2 liquid)

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• Group VIIA nonmetals

– halogens

– F, Cl, Br, I

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• Group VIA nonmetals

– Chalcogens

– O, S, Se, Te

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• Group VIIIA nonmetals

– noble, inert or rare gases

– He, Ne, Ar, Kr, Xe, Rn

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• Group 16 nonmetals - O, S, Se, Te

• Group 17 nonmetals -halogens

– F, Cl, Br, I, At

• Group 18 nonmetals -noble, inert or rare gases

– He, Ne, Ar, Kr, Xe, Rn

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• Group 13 – Boron

• Group 14 – Carbon

• Group 15 – Nitrogen

– Straddle the metal/ nonmetals

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CHAPTER 2chemphys.armstrong.edu/nivens/GeneralChemistry/CHapter2kotz.pdf · CHAPTER 2 Atoms and Elements 2 ... second letter lower case –C, Ca, Co –CO is not an element. 6. 7