chem unit 2

Democritus

Matter made of tiny individual particles called **ATOMOS**

\-Different kinds of atoms have different size and shape

John Dalton

Described the atom as a small, incompressible sphere with an atmosphere of heat

\-solid sphere atomic theory

Dalton’s solid sphere atomic theory

1. All matter is composed of extremely small particles called atoms.
2. All atoms of a given element are identical in size, mass and chemical properties.
3. The atoms of a given element are different from those of any other element
4. Atoms cannot be divided into smaller particles.
5. Atoms of one element can combine with atoms of other elements in whole number ratios to make compounds
6. Atoms cannot be created, divided, nor destroyed in a chemical reaction, just rearranged

J.J Thomson

credited with the discovery of the ELECTRON

\-plum pudding model

Ernest Rutherford

Conducts his famous experiment called the “Gold Foil Experiment.”

\-shot alpha particles at a thin sheet of gold foil.

\-expected most of the alpha particles to pass straight through the foil

\-nuclear model

Ernest Rutherford’s Nuclear Model (Planetary Model)

The atom is mostly empty space

\-tiny dense region (nucleus) contains all positive charge

James Chadwick

credited with discovery of the neutron

Nucleus

tiny dense region centrally located in atom containing all positive charge and virtually all it’s mass

Proton

charge of 1+

Neutron

no charge

Electron

charge of 1-

Structure of an Atom

An atom is electrically neutral.

\-# of protons = # of electrons

Atoms can gain or lose electrons

ion

\# of protons does not equal # of electrons

Atomic Number (Z number)

The number of protons in an atom

\-Periodic table arranged by increasing atomic numbers

\-Hydrogen has an atomic # of 1

Atomic Number = # of Protons = # of Electrons for atoms

Mass Number (A number)

The number of protons and neutrons in the nucleus

\-# of neutrons = mass number – atomic number

isotope

Elements may have different numbers of neutrons in \n nucleus

Isotopic Notation

nuclear notation

A number (mass number) = protons + neutrons

Z number (atomic number) = protons

The number of neutrons = A - Z

Atomic Mass

weighted average mass of the isotopes of that element

Mass contribution = (mass)(percent abundance)

Nuclear Reactions

Nuclear reactions differ from chemical reactions:

– Chemical: atoms attain stable electron configurations by losing or sharing electrons

– In nuclear reactions, the nuclei of unstable isotopes (radioisotopes) gain stability by undergoing changes

Basic Forces

There are 4 basic forces in the universe

\-Gravity

\-The electromagnetic force

\-The strong nuclear force

\-The weak nuclear force

Radioactivity

When strong force not strong enough to hold nucleus \n together, the nucleus will decay and give off matter \n and energy

\-decay of a nucleus is called radioactivity

Proton (symbols)

symbol = p⁺

nuclear symbol = ¹₁H

Neutron (symbols)

symbol = n⁰

nuclear symbol = ¹₀n

Electron (symbols)

symbol = e⁻

nuclear symbol = ₋₁⁰e

Alpha

symbol = a

nuclear symbol = ⁴₂He

Beta

symbol = b

nuclear symbol = ₋₁⁰e

Gamma

symbol = y / g

nuclear symbol = ⁰₀y

Results of Radioactivity

\-Release of energy

\-Emitting particles

\-This release of energy and particles is called radiation

There are 3 types of nuclear radiation

\n -Alpha (α)

\-Beta (β)

\-Gamma(γ)

Beta Particles (β)

\n In an unstable nucleus a neutron decays into a proton.

\-This releases an electron.

\-This released electron is a beta particle.

\-New element formed (# of protons changes) Called transmutation.

\-Mass # stays the same

\-decay is combined with ₋₁⁰e

Alpha Particles

helium nuclei that have been emitted from a radioactive \n source

\-Called alpha particles: contains two protons and two neutrons and has a double positive charge

\-decay is combined with ⁴₂He

Gamma Radiation

Most penetrating of radiation

\-Less damage to biological tissue

\-decay is combined with ⁰₀y

Comparison

\-Alpha: do not travel far and are not penetrating (a sheet of \n paper would stop them)

\-Beta: can pass through paper but are stopped by aluminum foil

\-Gamma: can pass through paper, wood, and the human body

Half Life

\-A measure of the time required by a nuclei to decay is \n called half life.

\-Half life is how long it will take one half of a radioactive \n isotope to decay.

Geiger counter

detects radiation