atoms, ions and molecules the building blocks of matterpostonp/ch221/pdf/ch02-w14.pdf · • from...

1/24/2018

1

Atoms, Ions and Molecules

The Building Blocks of Matter

Chapter 2

1/24/2018

2

Chapter Outline

2.1 The Rutherford Model of Atomic Structure

2.2 Nuclides and Their Symbols

2.3 Navigating the Periodic Table

2.4 The Masses of Atoms, Ions, and Molecules

2.5 Moles and Molar Mass

2.6 Making Elements

2.7 Artificial Nuclides

Experiments in Atomic Structure

• J. J. Thompson (1906 Nobel Prize in Physics)

- cathode ray tube experiments; discovery of the

electron; measurement of the charge-to-mass

ratio.

• Robert Millikan (1923 Nobel Prize in Physics)

- oil-drop experiments; measured the mass of the

electron, therefore calculate the charge

• Ernest Rutherford (1908 Nobel Prize in Physics)

- gold-foil experiments; the nuclear atom

• James Chadwick (1935 Nobel Prize in Physics)

- discovery of the neutron

1/24/2018

3

J.J. Thomson Cathode Ray Tube

Experiments - Electrons

Results of “Cathode Ray” Experiments

• Travel in straight lines

• invisible

• independent of cathode composition

• bend in a magnetic field like a

negatively-charged particle would

• charge/mass = -1.76 x 108 C/g

1/24/2018

4

Thompson’s “Plum Pudding” Model of the Atom

electrons distributed throughout a diffuse, positively charged sphere.

Robert Millikan’s oil drop Experiment -

measured the mass of the electron

1/24/2018

5

Millikan’s Results • The air molecules in the chamber were ionized by a beam of X-rays,

producing electrons and positively-charged fragments

• Fine mist of oil introduced into chamber; electrons adhere to the

droplets

• Negatively-charged droplets settle to bottom of chamber under

influence of gravity

• Charged repeller plates adjusted until droplets were suspended in

mid-air

• From the physics and knowledge of the size of the gravitational and

electrostatic forces, the charge on each droplet could be calculated

• Discovered that each droplet was a whole-number multiple of 1.60 X

10-19 C, so the mass = 9.11 X 10-28 g

Radioactivity and the Nuclear Atom

Spontaneous emission of particles and/or radiation from a

decaying, unstable nucleus

-particles =

-particles =

-rays =

1/24/2018

6

Ernest Rutherford - the nuclear atom

1/24/2018

7

Rutherford's Observations

1. the majority of particles penetrated undeflected

2. some particles were deflected at small angles

3. occasionally -particles scattered back at large angles

b) Expected results from “plum

pudding” model.

c) Actual results.

Rutherford’s Conclusions

• The atom is mainly empty space

because most of the -particles passed

through undeflected

• The nucleus is very dense and

positively charged because some of the

-particles were repulsed and deflected

• Electrons occupy the space around the

nucleus

• The atom is electrically neutral

1/24/2018

8

atomic radius ~ 100 pm = 1 x 10-10 m

nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m

Rutherford’s Model of the Atom

If the nucleus was the size of an orange, then the radius of the atom would

be 2.5 miles

mass p mass n = 1840 x mass e-

1/24/2018

9

Chapter Outline






2.6 Making Elements


Atomic Mass Units

• Atomic Mass Units (amu)

• Comprise a relative scale to express the

masses of atoms and subatomic particles.

• Scale is based on the mass of 1 atom

of carbon:

» 6 protons + 6 neutrons = 12 amu.

• 1 amu = 1 Dalton (Da)

1/24/2018

10

Isotopes: Experimental Evidence

Atomic number (Z) = number of protons in nucleus

Mass number (A) = number of protons + number of neutrons

= atomic number (Z) + number of neutrons

Isotopes (nuclides) are atoms of the same element with

different numbers of neutrons in the nucleus

X A

Z

Mass Number

Atomic Number Element Symbol

U 235 92 U 238

92

H 1 1 H (D)

2 1 H (T)

3 1

1/24/2018

11

• Use the format AX to write the symbol for the nuclides having 28 protons and 31 neutrons.

Practice: Isotopic Symbols

• Collect and Organize:

• Analyze:

• Solve:

• Think about It:

• Complete the missing information in the table.

Practice: Identifying Atoms and Ions

• Collect and Organize:

• Analyze:

• Solve:

• Think about It:

1/24/2018

12

Chapter Outline






2.6 Making Elements


Mendeleev’s Periodic Table

Dmitrii Mendeleev (1872):

• Ordered elements

by atomic mass.

• Arranged elements in

columns based on similar

chemical and physical

properties.

• Left open spaces in the

table for elements not yet

discovered.

The Periodic Table of the Elements

1/24/2018

13

The Modern Periodic Table

• Also based on a classification of elements in

terms of their physical and chemical

properties.

• Horizontal rows: called periods (1 → 7).

• Columns: contain elements of the same

family or group (1 →18).

• Several groups have names as well as

numbers.

Navigating the Modern Periodic Table –

Groups and Families

1/24/2018

14

Groups of Elements (cont.)

1/24/2018

15

These 7 elements occur naturally as diatomics (memorize) -

H2 N2 F2 O2 I2 Cl2 Br2

Metals

• found to the left of the “diagonal

line”

• lose electrons in chemical

reactions

• solids (except for Hg, Cs, and Fr)

• conduct electricity

• ductile (draw into a wire)

• malleable (roll into sheets)

• form alloys ("solid-solution" of

one metal in another)

1/24/2018

16

Nonmetals

• found to the right of the “diagonal line”

• like to gain electrons from metals, or

share electrons among themselves

• found as solids, liquids (Br), and gases

(Inert gases, and H, N, O, F, Cl)

• “diatomics” - H2, N2, F2, O2 ,I2, Cl2, Br2

• oxygen also exist as ozone, O3

• insulators (except for graphite or C)

Helium-Neon lasers

Metalloids

• elements next to the

“diagonal line”

• B, Si, Ge, As, Sb, and Te

• physical properties of a

metal (can be “convinced”

to conduct electricity) and

chemical properties of a

nonmetal Elemental Si is used in

the semiconductor

industry

1/24/2018

17

Chapter Outline






2.6 Making Elements


AM = (mass 1)(abn) + (mass 2)(abn) + (mass 3)(abn) +………

Average Atomic Mass

Weighted average mass of natural sample of an element,

calculated by multiplying the natural abundance of each

isotope by its exact mass in amu’s and then summing up

these products.

1/24/2018

18

Molecular Mass – the sum of the average atomic masses of the atoms in it.

NOTE: the terms mass and weight are used interchangeably, e.g. molecular weight (MW) or atomic weight (AW)

Molecular Mass

e.g. H2SO4

Formula Units – for ionic compounds,

the smallest electrically neutral unit in

an ionic compound

Formula Mass – the sum of the

average atomic masses of the cations

and anions that make up a neutral

formula unit

Formula Units and Formula Mass

e.g. NaCl

1/24/2018

19

Chapter Outline






2.6 Making Elements


The Mole - The mole is the Chemist’s

counting unit

Avogadro’s Number (NA) = 6.022 X 1023

= 1 mole of atoms, molecules, ions, etc.

pair = 2

dozen = 12

gross = 144

ream = 500

1/24/2018

20

One Mole of:

C S

Cu Fe

Hg

Experiment – how many atoms must be added together so that the mass in grams = mass in amu’s?

Analogy using coins:

Mass ratio = 1 : 5 : 25

1/24/2018

21

Significance of the Mole

NA of carbon atoms weighs __________

NA of iron atoms weighs __________

Mass in amu’s

Mass in grams/mole

Equivalent to

• To convert between number of particles

and an equivalent number of moles.

Moles, Mass, and

Particles

1/24/2018

22

Sample Exercise 2.5

The silicon used to make computer chips has to be

extremely pure. Fpr example, it must contain less than

3 x 10-10 moles of phosphorus (a common impurity in

Si) per mole of silicon. What is this level of impurity

expressed in atoms of phosphorus per mole of Si?

e.g. carbon e.g. H2SO4 sulfuric acid

Using the Molar Mass as a Conversion

Factor for Atoms & Molecules

12.011 grams

mole

1 mole

12.011 grams

98.0 grams

mole

1 mole

98.0 grams

1/24/2018

23

Moles, Mass, and

Particles

grams of

atoms or

molecules

moles of

atoms or

molecules

Numbers of

atoms or

molecules

(a) How many moles of K atoms are present in

19.5 g of potassium?

(b) How many atoms of K are there?

Practice: Mole Calculations #1

1/24/2018

24

How many moles are present in 58.4 g of chalk (CaCO3)?


The uranium used in nuclear fuel exists in nature

in several minerals. Calculate how many moles of

uranium are found in 100.0 grams of carnotite,

K2(UO2)2(VO4)2•3H2O.


1/24/2018

25


Convert 2.45 x 1018 molecules of KCl to grams

atoms, ions and molecules the building blocks of matterpostonp/ch221/pdf/ch02-w14.pdf · • from...

Documents