• No results found

Atoms, Ions and Molecules The Building Blocks of Matter

N/A
N/A
Protected

Academic year: 2021

Share "Atoms, Ions and Molecules The Building Blocks of Matter"

Copied!
16
0
0

Loading.... (view fulltext now)

Full text

(1)

Atoms, Ions and Molecules The Building Blocks of Matter

Chapter 2

(2)

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

(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 10

8

C/g

(4)

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

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

Radioactivity and the Nuclear Atom

Spontaneous emission of particles and/or radiation from a decaying, unstable nucleus

-particles =

-particles =

-rays =

(6)

6 Ernest Rutherford - the nuclear atom

(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

(8)

8

atomic radius ~ 100 pm = 1 x 10-10m nuclear radius ~ 5 x 10-3pm = 5 x 10-15m

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-

(9)

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

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)

(10)

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 (X) with

different numbers of neutrons in the nucleus

A

X

Z

1

H

1 21

H (D)

31

H (T)

235

U

92 23892

U

Mass Number

Atomic Number Element Symbol

(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:

(12)

12

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

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

(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

(14)

14

Groups of Elements (cont.)

(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)

(16)

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, 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

References

Related documents

The following pages contain lists of Absent friends who died after June 2017.. Our sincere sympathy goes to

problematikken. Ikke minst har dette blitt erfart på den vanskelige måten ved at kollegaer har måttet gå som følge av nedskjæringer. Det kan allikevel stille spørsmålstegn ved om de

We demonstrated that Nrf2 deficiency enhanced mitochon- drial ROS production in aged skeletal muscle and exacer- bates age-related oxidative stress, but has little effect

ser lesiones destructivas u osteolíticas, osteoblásticas, expansivas y proliferativas, observándose como signos radiológicos: osteolisis, osteoesclerosis o ambas, reacción

In a process of three interventions spread over one year, the members of the new board clarified their own view of the governance network in which they are going to operate,

experiment, induced more severe skin lesions with thicker epidermis and dermis and higher levels of mast cell and neutro- phil infiltration, compared to WT mice ( Figures 2

Međutim, u toj definiciji nije sadržano da je to zapravo proces koji se iznova pokreće pa sukladno tome predlaže se sljedeća definicija kontrolinga: Kontroling

L’ensemble "bulle à bulle" se compose d’un coffret polyester et d’une canne de bullage. Un générateur d’air crée dans la canne de bullage une pression qui s’oppose à