Atoms, Molecules, & Ions

greeks

first to attempt to explain why chemical changes occur.

2000 years

how many years alchemy dominated

•Greeks were the first to attempt to explain why chemical changes occur.

▪Alchemy dominated for 2000 years.

▪Several elements discovered.

▪Mineral acids prepared.

▪Robert Boyle was the first “chemist”.

▪Performed quantitative experiments.

▪Developed first experimental definition of an element.        

events in the Early History of Chemistry

Robert Boyle

who was the first “chemist”

Law of Conservation of Mass (Lavoisier)

Mass is neither created nor destroyed in a chemical reaction.

Law of conservation of mass (Lavoisier)

Law of definite proportion (Proust)

Law of multiple proportions (Dalton)

3 important laws

Law of Definite Proportion (Proust)

A given compound always contains exactly the same proportion of elements by mass.

Law of Multiple Proportion (Dalton)

When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.

Dalton’s Atomic Theory

Each element is made up of tiny particles called atoms.

1808

what year is dalton’s atomic theory

Dalton’s Atomic Theory (continued)

The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways.

Dalton’s Atomic Theory (continued)

Chemical compounds are formed when atoms of different elements combine with each other.  A given compound always has the same relative numbers and types of atoms.

Dalton’s Atomic Theory (continued)

Chemical reactions involve reorganization of the atoms; The atoms themselves are not changed in a chemical reaction.

(1809—1811)

what year is Gay-Lussac and Avogadro

Gay-Lussac

Measured (under same conditions of T and P) the volumes of gases that reacted with each other.

Avogadro

At the same T and P, equal volumes of different gases contain the same number of particles.

▪Volume of a gas is determined by the number, not the size, of molecules.

J.J Thompson

Postulated the existence of negatively charged particles, that we now call electrons, using cathode-ray tubes.

1898-1903

year of j.j thomson

J.J Thomson

Determined the charge-to-mass ratio of an electron.

J.J Thomson

The atom must also contain positive particles that balance exactly the negative charge carried by electrons.

anode

postive charge

collects electrons

carhode

negative charge

releases electrons

Robert Milikan

Performed experiments involving charged oil drops.

1909

year of Robert Milikan

Robert Milikan

Determined the magnitude of the charge on a single electron.

▪Calculated the mass of the electron

9.11 × 10^-31 kg

mass of an electron

Henri Becquerel

Discovered radioactivity by observing the spontaneous emission of radiation by uranium.

1896

year of Henri Becquerel

gamma rays

beta particles

alpha particles

Three types of radioactive emission exist:

gamma rays

high energy light

beta particles

a high speed electron

alpha particle

a particle with a 2+ charge

Ernest Rutherford

Explained the nuclear atom.

▪The atom has a dense center of positive charge called the nucleus.

▪Electrons travel around the nucleus at a large distance relative to the nucleus.

1911

year of Ernest Rutherford

Niels Bohr

Proposed that electrons traveled in fixed paths around the nucleus.

1913

when Niels Bohr

to show the number of electrons in each orbit around the nucleus.

what is the reason why the scientists use Bohr model

Bohr was trying to show why the negative electrons were not sucked into the nucleus of the atom

why did bohr conducted his study

electron cloud model

Electrons travel around the nucleus in random orbits.

electron cloud model

Scientists cannot predict where they will be at any given moment.

electron cloud model

Electrons travel so fast, they appear to form a "cloud" around the nucleus.

Isotopes

Atoms with the same number of protons but different numbers of neutrons.

Isotopes

Show almost identical chemical properties; chemistry of atom is due to its electrons.

Isotopes

In nature most elements contain mixtures of isotopes.

atomic number

mass number

Isotopes are identified by

atomic number (Z)

number of protons

mass number (A)

In nature most elements contain mixtures of isotopes.

covalent bonds

Bonds form between atoms by sharing electrons.

molecules

Resulting collection of atoms

Ionic Bonds

Formed by the transfer of electrons from one atom to another.

Ionic Bonds

Bonds form due to force of attraction between oppositely charged ions.

Ion

atom or group of atoms that has a net positive or negative charge.

cation

positive ion; lost electron(s).

Anion

negative ion; gained electron(s).

Met

Found in metals

▪Metal atoms share a “sea” of free moving electrons.