Conceptual Physics The Atomic Nature of Matter

Atoms•Building blocks of matter•Everything is composed of atoms

Elements•atoms of the same kind•there are 115 known elements to date•Every element is unique, and has its own

set of properties•All atoms of the same element have the

same # of protons.

Atoms are recyclable•the same atoms have been here since the

beginning of time•Combine w/ other elements, then go back

to original form and back again•You may be breathing the same air as

Julius Caesar or George Washington….

Atoms are very small•Cannot view individual atoms w/ visible

light•Only way to “see” atoms is w/ Scanning

Tunneling Microscope•About 1023 (or

1000000000000000000000000000) atoms in one thimble-full of water

Brownian Motion•Jiggling of atoms•Atoms are constantly moving•Molecular motion never stops unless a

substance is at a temperature of (-273˚ C) a.k.a. absolute zero

Molecules•combinations of atoms ex. H2, H2O, NaCl,

N2

•Can be combinations of the same atom, or of different types of atoms

Compounds

•combinations of atoms of different elements ex. NaCl, H2O, HCl

•A compound is always a molecule, but a molecule may not necessarily be a compound (examples …. H2 , N2 )

Rutherford Experiment•Gold Foil - showed atoms are largely

empty space, very dense nucleus that reflected charged particles backwards

•Like a “shooting a 15-inch artillery shell at a piece of tissue paper and having it come back and hit you”

Nucleus

•very dense……. Composed of Protons & Neutrons

•Almost all of the mass of an atom is concentrated in the nucleus

•A teaspoonful of nuclei packed together would weigh a billion tons

Neutrons & Protons•Nuetrons- Nuetral charged particle

found in nucleus•Protons- Positively charged particle

found in nucleus, atoms of the same number of protons are atoms of the same element

Isotopes

•for a given element, the number of neutrons may vary. Isotopes of an element are atoms of the same element having different numbers of neutrons

•Example - Uranium-238 (atomic mass 238) has isotope Uranium -235▫This was used to make the atomic bomb

dropped on Hiroshima

Electrons (e-)•negatively charged particle not found in the

nucleus. •Orbits the nucleus in various energy levels. • In a neutral atom, the number of electrons will

match the number of protons•# of electrons in a neutrally charged atom is

equal to the # of protons, which is given with the atomic number.

•Mass of 1 electron is about 1800 times less than the mass of a proton or neutron

Ions•Charged Particle

▫Positively charged (less electrons than protons)

▫Negatively charged (more electrons than protons)

•not all atoms are neutral. This happens when the number of electrons is more than, or less than the number of protons. ▫The number of protons never changes, ▫however the number of electrons can

change often.

Shell Model of an Atom•Electrons occupy different shells. •2 maximum electrons may fit in the first

shell •The next shell holds 8 electrons, and the

largest shell will hold 32 electrons. •For example, if an atom has 13 electrons,

it will have 2 in the first shell, 8 in the second shell, and the remaining 3 will go in the third shell.

Periodic Table•chart that lists atoms by their atomic

number and by their electron arrangement.

•As you move from left to right on chart each element gains one proton and electron .

•As you go down each column each element has one more shell filled than the element above.

•Elements in the same column are in a Group. Groups have similar properties.

•Atomic Number - number of protons in the nucleus

•Atomic Mass – equals the average mass (in atomic mass units) of the nucleus▫# of Protons = Atomic Number▫# of Electrons = # of Protons, (if molecule has

no charge)▫# of Neutrons = (Atomic mass (rounded)) - (atomic

number)

Phases of Matter•Solid, Liquid, Gas – three familiar states

of matter. In all phases, atoms are in constant motion.

•The more the molecules move the more fluid they become,▫Solid – molecules have least energy, stay

fixed relative to each other▫Liquid- molecules have more energy,

molecules move relative to one another▫Gas – molecules have most energy, move

with large distances between each other

Plasma – the 4th State of Matter• Consists of positive ions and free

electrons. Exists only at high temperatures.

•What sun and stars are made of. Can be seen here on Earth in the glowing gas of fluorescent lamps.