RAD Principles of Physics 4

Greek Atom

An atom is the smallest particle that has all the properties of an element

Greeks thought that matter was made of what four substances?

earth, water, air, and fire

Greeks thought that matter was a combination of what four essences?

wet, dry, hot, and cold

Dalton atom

All elements are arranged into 8 groups as shown in the periodic table

What did Dmitri Mendeleev contribute?

the first periodic table of elements

Thomson atom

described the atom as looking something like a plum pudding, in which the plums represented negative electric charges (electrons) and the pudding was a shapeless mass of uniform positive electrification. The number of electrons was thought to equal the quantity of positive electrification because the atom was known to be electrically neutral.

Ernest Rutherford

in 1911 disproved Thomson’s model of the atom. Introduced the nuclear model, which described the atom as containing a small, dense, positively charged center (the nucleus) surrounded by a negative cloud of electrons.

Bohr Atom

1913, Niels Bohr improved Rutherford’s description of the atom. Bohr’s model was a miniature solar system in which a small, dense, positively charged nucleus surrounded by negatively charged electrons that revolve in fixed, well-defined orbits about the nucleus. In the normal atom, the number of electrons is equal to the number of positive charges in the nucleus.

What are the fundamental particles of an atom?

electron, proton, and neutrons

Electrons

are very small particles that carry one unit of negative electric charge

Electron mass

9.1 × 10^-31 kg or 0.000549 amu

Where is the electron in the bohr model?

revolving about the nucleus in precisely fixed orbits

atomic mass units (amu)

equal to one-twelfth the mass of a carbon-12 atom

atomic mass number

When precision is not necessary, a system of whole numbers

atomic mass number of electron

0

mass of proton

1.673 × 10^-27 kg

mass of neutron

1.675 × 10^-27 kg

the atomic mass of protons and neutrons is

1

proton carries?

one unit of positive electric charge

neutron carries?

no charge; it is electrically neutral

The atom is essentially ??? space?

empty

atoms are electrically ?

neutral

electric charge of an atom is

0

Electron arrangment

Maximum Electrons Per Shell = 2n² where n is the shell number

Isotopes

Atoms that have the same number of protons but differ in the number of neutrons

What determines the chemical element?

the number of protons

The number of electrons in the outer shell is

equal to its group in the periodic table and determines the valence of an atom

The number of the outermost electron shell is

equal to its period in the periodic table

Ionized electron

If an atom has an extra electron or has had an electron removed

Can atoms be ionized by changing the number of positive charges?

No, atoms cannot be ionized by the addition or subtraction of protons because they are bound very strongly together, and that action would change the type of atom

Can atoms be ionized by changing the number neutrons?

No, an alteration in the number of neutrons does not ionize an atom because the neutron is electrically neutral

No outer shell can contain more than ??? electrons?

8

Transitional elements

The orderly scheme of atomic progression from smallest to largest atom is interrupted in the fourth period. Instead of simply adding electrons to the next outer shell, electrons are added to an inner shell.

Centripetal force

the force that keeps electrons in orbit

the centripetal force just balances the force created by the electron velocity, ???, so that electrons maintain their distance from the nucleus while traveling in a circular or an elliptical path

Centrifugal force

Electron binding energy

the strength of attachment of an electron to the nucleus

Ionization potential is

34 eV

atomic mass number

The number of protons plus the number of neutrons in the nucleus of an atom

The atomic mass number and the precise mass of an atom are

NOT equal

actual atomic mass

determined by measurement and rarely is a whole number

Isotopes

Atoms that have the same atomic number but different atomic mass numbers are isotopes.

Isobar

Atomic nuclei that have the same atomic mass number but different atomic numbers

Isotones

Atoms that have the same number of neutrons but different numbers of protons

Isobaric radioactive transitions from

parent atom to daughter atom result from the release of a beta particle or a positron.

The parent and daughter of an isobar are atoms of ??? elements?

different

Isomer

have the same atomic number and the same atomic mass number.

Molecule

Atoms of various elements may combine to form structures

Chemical compound

any quantity of one type of molecule

Radioactivity

the spontaneous emission of particles and energy in order to become stable

Radioisotopes

Radioactive isotopes

Radioactive decay results in

results in emission of alpha particles, beta particles, and usually gamma rays

Radioactive half-life of a radioisotope

the time required for a quantity of radioactivity to be reduced to one-half its original value

Particulate radiation

alpha and beta particles

alpha particles

a helium nucleus that contains two protons and two neutrons

alpha particle mass

4 amu

the alpha particle is large and exerts great

electrostatic force

Alpha particles are emitted ONLY from

the nuclei of heavy elements

beta particles are emitted from

from the nucleus of a radioactive atom

Beta particle mass

O

Beta particle

are light particles, and they carry one unit of negative or positive charge

X-rays and gamma rays are often called

photons

Gamma rays come

from the nucleus

X-rays come from

the electron cloud