General Chemistry Chapter 2

Atom

An atom is the smallest quantity of matter that still retains the properties of matter.

Element

An element is a substance that cannot be broken down into two or more simpler substances by any means.

• Examples: gold, oxygen, helium.

Dalton

atoms, of which all matter consists, are tiny, indivisible particles.

Once a single atom has been obtained, dividing it smaller produces subatomic particles.

Tool commonly used in the 1800s

cathode ray tube,

Cathode Ray Tube and Radiation

Radiation is energy emitted through space as waves. A cathode ray tube passes voltage across metal plates in a vacuum, emitting invisible rays from the cathode to the anode.

Fundamental Rule of Electrostatic Charges

Like charges repel each other, and opposite charges attract one another.

J.J. Thomson's Atomic Discoveries

Discovered electrons (negatively charged particles in cathode rays) and calculated their charge-to-mass ratio as 1.76×108 C/g.

R.A. Millikan's Oil Drop Experiment

Determined the fundamental charge of a single electron to be −1.6022×10−19 C.

Mass of an electron

 

Who discovered X-rays They were not deflected by magnetic or electric fields, so they could not consist of charged particles.

Wilhelm Rontgen (18 45–19 23).

discovered radioactivity the spontaneous emission of radiation.

Antoine Becquerel (18 52–19 08)

Alpha (α) rays consist of

positively charged particles, called α particles

Beta (β) rays, or β particles, are

electrons so they are deflected away from the negatively charged plate

Gamma (γ) rays, like X rays, have

no charge and are unaffected by external electric or magnetic fields

Ernest Rutherford used α particles to

prove the structure of atoms.

The majority of particles penetrated the gold foil undeflected.

Sometimes, α particles were deflected at a large angle.

Sometimes, α particles bounced back in the direction from which they had come.

Protons are

positively charged particles found in the nucleus.

Neutrons are

electronically neutral particles found in the nucleus.

Neutrons are

slightly larger than protons.

Electrons are

negatively charged particles distributed around the nucleus.

Electron

Particle	Mass (g)	Mass (amu)	Charge (C)	Charge Unit
Electron*	9.10938 × 10 superscript -2	5.4858 × 10superscript -4	−1.6022 × 10superscript -19	−1

Proton

Particle	Mass (g)	Mass (amu)	Charge (C)	Charge Unit
Proton	1.67262 × 10superscript minus-4	1.0073	+1.6022 × 10superscript -19	+1

Neutron

Particle	Mass (g)	Mass (amu)	Charge (C)	Charge Unit
Neutron	1.67493 × 10superscript minus-24	1.0087	0	0

atomic number (Z) is

the number of protons in the nucleus.

Atoms are neutral, so it’s also the number of electrons

mass number (A) is

the total number of protons and neutrons.

Element symbol(Atoms are neutral so the number of electrons equals the number of protons.)

Atomic mass is

the mass of an atom in atomic mass units (a m u).

Measuring Atomic Mass

The most direct and most accurate method for determining atomic and molecular masses is mass spectrometry, using a  mass spectrometer.

The periodic table is

a chart in which elements having similar chemical and physical properties are grouped together.

Metals are

good conductors of heat and electricity.

Nonmetals are

poor conductors of heat or electricity.

Metalloids have

intermediate properties.

Group 1 elements (L i, N a, K, R b, C s, F r) are called

alkali metals

Group 2 elements (B e, M g, C a, S r, B a, R a) are called

alkaline earth metals.

Group 16 elements (O, S, S e, T e, P o) are called .

chalcogens

Group 17 elements (F, C l, B r, I, A t) are called .

halogens

Group 18 elements (H e, N e, A r, K r, X e, Rn) are called .

the noble gases

Groups 3 to 11 are called the .

transition elements or transition metals