Chapter 2

Chapter 2 - Chapter 2 Small Molecules and the Chemistry of...

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Chapter 2 – Small Molecules and the Chemistry of Life 2.1 – How does atomic structure explain the properties of matter? Mass of proton = standard unit of measure o 1 proton = 1 Dalton [Da] = 1 amu = 1.7x10 -24 g o 1 electron = 0.0005 Da = 0.0005 amu = 9x10 -28 g Mass of electron is negligible compared to neutron o Element is a substance that has only one kind of atom Stars are mostly hydrogen and helium Earths crust is ~50% O, 28% Si, 8% Al, 2-5% Na Mg K Ca Fe 98% of living mass is made of C H O N P S Mass number has both numbers of neutrons and protons, so it changes with isotopes Carbon comes mostly in C12, 1.1% C13 and tiny amounts of C14 Atomic weight is the average of the mass numbers of a representative sample of atoms of that element, with all the isotopes in their normally occurring proportions Most isotopes are stable, but some isotopes, known as radioisotopes, give of alpha, beta or gamma radiation from the atomic nucleus (known as radioactive decay) Through radioactive decay, the radioisotope may give off protons, becoming a different element An orbital is the region of space where a certain electron is found 90% of the time Orbitals are filled in a specific sequence of what are known as electron shells or energy levels found around the nucleus First shell is the s, it can hold 2 electrons Second shell is the s (two again) and the p, which can hold up to six electrons. So 8 all together Atoms that have three or more electron shells have higher energy levels for the electrons in farther shells The valence shell dictates how the atom will interact chemically Hydrogen is an exception to the octet rule, it is stable with only 2 electrons (1 s orbital) 2.2 – How do atoms bond to form molecules? Covalent bonds occurs when 2 atoms attain stable electron numbers in their valence
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Chapter 2 - Chapter 2 Small Molecules and the Chemistry of...

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