Chem 3

law of definite proportions

the law that states that a chemical compound always, contains the same elements in exactly the same proportions by weigh or mass

law of conservation mass

mass cannot be created or destroyed in ordinary chemical and physical changes

law of multiple proportions

when two elements combine to form two or more compound, the mass of one element that combines with a given mass of the other is in the ratio of small whole numbers

Daltons 5 principles

1. all matter is composed of atoms, which cannot be subdivided, created or destroyed

2. atoms of a given elements are identical in their physical and chemical properties

3. atoms of different elements differ in their physical and chemical properties

4. atoms of different elements combine in simple, whole number ratios to form compounds.

5. in chemical reaction, atoms are combines, separated or rearranged but never created, destroyed or changed.

compound

substance that is made of two or more different elements that are chemically bonded together in a fixed ratio

alpha particle

a small, positively charged particle, which Rutherford directed at thin, gold foil

anode

the electrode attached to the negative terminal of a voltage source

atomic number

the number of protons that compose the nucleus of an atom; this number is the same for all atoms of an elemnt

cathode

an electrode attached to the positive terminal of a voltage source

coulomb’s law

states that the closer two charges are, the greater the force between them; in fact, the force increases by a factor of 4 as the distance is halved

electron

a subatomic particle that has a negative charge

proton

a subatomic particle that is positively charged and is equal to the atomic number of an element. It is located in the nucleus. The number of these particles determine an element

isotope

an atom that has the same number of protons as other atoms of the same element but has a different number of neutrons

mass number

the sum of the number of protons and neutrons of the nucleus of an atom

Thomson’s cathode ray experiment

Thomson believed the rays were particles because a paddle wheel was set into motion by the ray. He concluded that the beam was negatively charged because the ray came from the negative electrode.

describe the evidence for the existence of electrons

Thomson's experiments showed that a cathode ray consists of particles, called electrons, that have mass and a negative

describe the evidence for the existence of protons

Positively charged particles in the nucleus, called protons, repel alpha particles in gold-foil experiments.

describe the evidence for the existence of neutrons

Protons and electrons have equal but opposite charges, but the mass of atoms is greater than the mass of the protons and electrons. Other particles, called neutrons (which have no electrical charge), accounted for the missing mass

J.J Thompson

discovered the electron through cathode rays. He also demonstrated that atoms were not visible but composed of smaller subatomic particles. He also established the plum pudding model of the atom

Rutherford

suggested that electrons orbit the nucleus in elliptical orbits. It had to be replaced because it wouldn’t explain why the electrons did not crash into the nucleus.

Ions

Ions are atoms or molecules that have gained or lost one or more electrons, resulting in a net electrical charge.

cations

hese are positively charged ions formed when an atom or molecule loses electrons. For example, a sodium atom (Na) loses one electron to form a Na⁺ cation.