chem study guide

Who discovered that the center of the atom was very small and dense with an overall positive charge in his gold foil experiment?

Rutherford

What is the subatomic particle with a positive charge called?

Proton

The __ is always equal to the number of protons + the number of neutrons that the atom has.

Mass number

An atom that gains an electron will have a charge.

Negative

According to Dalton, atoms of different elements will be .

Different

The of an element is the weighted average of the masses of the different isotopes of that element.

Atomic mass

What is found in the atom's nucleus?

Neutrons and protons

Atomic # of an atom =

Protons

What is approximately the mass of a proton?

1 amu (atomic mass unit)

What did Thomson discover in his cathode ray experiment?

The electron

What are atoms that have the same atomic number but different mass called?

Isotopes

What did Democritus say were the indivisible, fundamental units of matter?

Atoms

An anion is an atom with an overall charge.

Negative

An atom gets an overall positive charge by what?

Losing electrons

Explain the whole major point of Dalton’s atomic theory.

All elements are made of tiny, invisible atoms; atoms of the same element are the same, and atoms of different elements are different; atoms of different elements can combine in whole number ratios to make compounds; in chemical reactions, atoms are rearranged, and atoms of one element are never changed into another element.

What is the Rutherford Gold foil experiment?

He shot a high beam of alpha particles into gold foil. Most particles went straight through → atoms are mostly space; Some deflected at small angles → there's a small positive center; A few bounced back → atoms have a tiny, dense, positive nucleus.

How did Thomson know the charge of the particle he discovered was negative?

Because the particles in the gas were attracted to the positive plate, he assumed the particles had a negative charge due to the theory that opposites attract.

Compare and contrast ions and isotopes. What subatomic particle changes in each?

Ions – atoms with a charge; Isotopes – atoms of the same element, but with different masses. In ions, electrons change; in isotopes, neutrons change.

What is the difference between atomic mass and mass number?

Atomic mass is a weighted average; the mass number is protons + neutrons and should be a whole number.