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Atomic Structure notes
Atom – the smallest part of an element that still has the properties of that element. Cannot be divided any smaller and still
retain its identity.
I.
Parts of the atom
Nucleus – the center of the atom- is not a “control center” like a cell’s nucleus. It contains two subatomic
particles: the protons and the neutrons. (They are combined and form a nucleus the nucleus is not surrounded by a
membrane)
Electron Cloud – is the name of the space outside the nucleus where the electrons orbit around. The cloud is
composed of empty space besides the few electrons rotating in it.
II.
Subatomic particles
Protons (Found by Henry Moseley)– Found in the nucleus. The identity of an atom/element is due to the protons.
They carry a mass number of 1amu and a positive 1+ charge. The number of protons in an atom of a given
element CAN NOT vary.
Neutrons (Found by Chadwick)
– Found in the nucleus. These particles hold the nucleus together, (since protons are all positive they would repel
each other if they had nothing to hold them). They carry a mass number of 1amu and have no charge, are neutral.
Neutrons can vary in an atom.
Quarks – The particles of matter that make up protons and neutrons, 3 quarks make up a proton, 3 quarks make
up a neutron. There are 6 types, “flavors”, Up/down, Charm/strange, Top/bottom. Up/down make up the protons and
neutrons. Two ups and 1 down make a proton, two downs and 1 up make a neutron. (held together by gluons)
Electrons – These particles are very small, they affect how the atoms react and bond, they exist in seemingly
random points in the electron cloud. They carry a mass number of 0amu and a negative -1 charge. Electrons can
be shared with/traded to other atoms. ( located in the electron cloud)
III.
Atomic Vocab
Atomic number- the number above the element in the periodic table, tells us the number of protons in an atom.
Atomic mass number – the number of protons and neutrons in a given atom. (each have a mass of 1amu)
Example: All carbon atoms have 6 protons, most carbon atoms have 6 neutrons – these atoms have a mass of 6p +
6n = 12. Some carbons have 7 neutrons – these atoms have a mass of 6p + 7n = 13. And some even have 8
neutrons – these atoms have a mass of 6p + 8n = 14.
Average atomic mass (found on periodic table)AKA Molar mass – a weighted average of all of the various atoms of a
given element
Orbital – the space around an atom where the electron rotates.
Ions – these are atoms that carry a charge because they have either gained or lost an electron.
Cation – positive ion (atom), lost electrons
Anion- negative ion (atom), gained electrons
Isotopes – these are atoms that have more or less neutrons than the most common atom of a given element. Since they
have more or less neutrons, they have more or less mass than the common atom.
Isotopes can be shown by telling the name followed by a dash and their mass number .
Ex. Carbon–13
Carbon-14
Extra
Charge – a comparison of the protons and electrons in an atom. More protons means the atom has more positives
and thus has a positive charge. More electrons means the atom has more negatives and thus has a negative charge.
Charge = (protons x (+1)) + (electrons x (-1))