CEM 141 Chapter 1 Learning Objectives
Atoms: the smallest unit of ordinary matter that forms a chemical element
Molecules: electrically neutral group of two or more atoms held together by chemical bonds.
Elements: consists only of the same atoms, with the same number of protons
Compounds: a chemical substance composed of atoms from 2+ elements held together by
chemical bonds - ANS-Identify and explain the similarities and differences between atoms,
molecules, elements, and compounds
Attraction between two atoms is caused by London dispersion forces created by the random
and chaotic movement of electrons. This is because the electrons in an electron cloud is not
always proportional, sometimes because of their chaotic movement, electrons can bunch up
more on one side of the nucleus than the other, creating an instantaneous dipole. This creates a
PARTIAL +/- charge within the atom. This causes the electron cloud of a neighboring atom in
the isolated system to be attracted to the partial + charge. This is the induced dipole. This
attracts the two atoms and they approach each other. However, as they get extremely close, the
electron clouds of the two atoms begin to overlap, so the electrons of both atoms are repelled
by each other because they are both negative. As they move even closer, the repulsive force
will overcome the attractive one because the close electrons want to move away, causing them
e - ANS-construct an atomic level explanation for why two isolated atoms would attract each
other as they approach, and why they would repel if they get too close together
bigger the atom, stronger the LDFs because the electrons clouds are bigger and hold more
electrons, hence floppier, which makes for more distortion/dipoles. there is also a larger surface
area of bigger atoms which makes for more area to interact - ANS-predict/rank the relative LDFs
between atoms and molecules of different sizes
Claim: a nucleus is a subatomic particle inside an atom.
Evidence: Rutherfords experiment using helium atoms which he projected onto a gold foil.
Reasoning: most of the particles(He atoms) went straight through the foil. However, some atoms
were deflected off the foil and an even smaller amount bounced right back to where they were
initially projected from. This is because of the bigger nuclei inside gold atoms which the He at
times would come into contact with, causing them to deflect. The nucleus must exist or else the
He atoms would not have been deflected, and all of them would have gone straight through.
(nucleus positive because electrons of He repel it, it is small because MOST went through) -
ANS-Make an argument(claim, evidence, reasoning) for the existence of the existence of a
small, massive, and positively charged nucleus
Claim: atoms are the smallest unit of matter that forms an element and make up everything in
the world
Evidence: an example is water, which is a liquid we drink and makes up more than half our
body.
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