Atomic Structure ReviewAC Physical Science

2008

Atom, Molecule, or Compound ??

• Atoms - smallest particle of an element• Element – cannot be broken down by any

means possible• Molecule – 2 or more atoms that are

bonded together. For example O2 and H2O.

• Compounds – substance made of 2 or more elements. For example: H2O

• ALL compounds are also molecules, BUT all molecules ARE NOT compounds… WHY??

Elements…

• Cannot be separated into simpler substances by any chemical or physical means.

• Pure Substances are substances where there is only one type of particle – for example pure oxygen.

• Elements have their own unique properties, but can share characteristics.

Classifying Elements

• Classified by their properties…

• Categories are defined as metals, nonmetals, and metalloids.

• Samples of metals = Pb, Cu, Sn

• Samples of nonmetals = S, Ne, I

• Sample of metalloids = Si, B, Sb

Molecules

• 2 or more atoms that are combined together

• Example = O2

Compounds

• A Compound is a pure substance composed of 2 or more elements that are chemically combined.

• Examples: CO2

Mixtures

• Combination of 2 or more substances that are not chemically combined

• Solutions – mixture that appears to be a single substance – composed of 2 or more substances that are evenly distributed among each other.

• Solute – substance that is dissolved• Solvent – substance in which the solute

is dissolved in

Mixtures continued…

• Concentration – measure of the amount of solute dissolved in a solvent

• Solubility – solutes ability to dissolve in the solvent at a certain temperature

• Suspension – mixture in which particles of a material are dispersed throughout a liquid or gas (example Italian Salad Dressing)

• Colloid – mixture consisting of tiny particles that are dispersed throughout, but are not heavy enough to settle out (Example = jello or milk)

Atoms..

• Atom = the smallest particle an element can be divided into and still be the same substance.

• Atom is from the Greek word atomos, meaning “not able to be divided”.

Dalton’s Atomic Theory• John Dalton, a British chemist

published his theory in 1803.

• His theory states the following ideas:– All substances are made of atoms. Atoms

are small particles that cannot be created, divided, or destroyed.

– Atoms of the same element are exactly alike, and atoms of different elements are different.

– Atoms join with other atoms to make now substances.

Not quite correct…

• 1897, J.J. Thomson showed that there was a mistake in Dalton’s theory.

• He discovered that there are smaller particles inside the atom.

• Which means that the atom can be divided into even smaller parts.

• Thomson discovered negatively charged particles that are called electrons.

Rutherford’s Atomic “Shooting Gallery”

• In 1909, Ernest Rutherford tested Thomson’s Theory.

• He aimed a beam of small positively charged particles at a thin sheet of gold foil.

• In 1911, Rutherford revised the atomic theory. He made a new model.

• He proposed that the center of an atom is tiny, extremely dense, and positively charged part called the nucleus.

• Because like charges repel, a particle that headed straight for a nucleus would be pushed almost straight back and in the direction in which it came.

Bohr’s Electron Level

• In 1913, Niels Bohr, worked with Rutherford, And studied that way that atoms react to light.

• The results led him to propose that electrons move around the nucleus in certain paths or energy levels.

• Bohr’s model was a valuable tool in predicting some atomic behavior, but the atomic theory still had room for improvement.

The Modern Atomic Theory

• Erwin Schrödinger and Werner Heisenberg work and further explained that nature of electrons in an atom.

• The determined that the exact path of an electron cannot be predicted.

• According to the current theory, there are regions inside the atom where electrons are likely to be found.

• These regions are called electron clouds.

Electron Clouds…

• Use the formula 2(N2) to determine how many electrons fit in each cloud…

Practice, Practice…

Parts of an Atom

• Nucleus: the small dense positively charged center of the atom.– This contains most of the atom’s mass.

• Protons: are positively charged particles in the nucleus of an atom

• Neutrons: are particles in the nucleus that have no charge.

• Electrons: negatively charged particles found in the electron clouds outside the nucleus.

Subatomic Particles…

• Protons are positive +

• Neutrons are neutral

• Electrons are negative –

• Protons and neutrons are in the center of the nucleus

• Electrons are situated in electron clouds spinning around the nucleus

Things to remember…

• Atomic Number = the number of protons and electrons

• The difference between the atomic number and the atomic mass = the number of neutrons

The Nucleus

• Protons: are positively charged particles in the nucleus of an atom

• The SI unit used to express the masses of particles in atoms is the:

atomic mass unit (amu)– Each proton has a mass of about 1amu

• Neutrons: are particles in the nucleus that have no charge.

Outside the Nucleus• Electrons: negatively charged particles

found in the electron clouds outside the nucleus.

• Compared with protons and neutrons, electrons are very small in mass.

• The charges of protons and electrons are opposite, but equal, so they cancel each other out.

• Because an atom has no overall charge, it is neutral.

• What happens if the numbers of the electrons and protons are not equal?...

Well…Ions…• The atom becomes a charged particle

called an ion.

• An ION is an atom or group of atoms that carry an electric charge.

• So…if an atom has more protons it is???

• If there are more electrons??

• This is how weather patterns are created…

Isotopes• An atom that has the same number or

protons (or the same atomic number) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mass).

• You can tell Isotopes apart by the mass number which is the sum of the numbers of protons and neutrons in the nucleus of an atom. Example of an Isotope = Carbon-14 used to date rocks…

How do I find Neutrons again?

• The difference between the atomic number and the atomic mass = the number of neutrons