Chemistry Midterm 1

Dalton’s Atomic Theory First Postulate

Atoms of different elements have different masses (yes) and are indivisible (no)

• Generally have different masses, although the masses can be very similar to each other (such as argon-40 and calcium-40; atoms of different elements can have nearly the same mass)

Dalton’s Atomic Theory Second Postulate

Atoms of a given element have the same mass (no) and other properties (semi)

• Isotopes

• Chemical properties among isotopes are determined by valence electrons rather than amount of neutrons

• Physical properties, such as density, stability, and radioactivity, are different

Dalton’s Atomic Theory Third Postulate

Atoms retain their identities through chemical reactions (no)

• In nuclear reactions, an atom can change their identity through gaining a proton

Dalton’s Atomic Theory Fourth Postulate

Atoms always combine in whole-number integers when forming compounds (no)

• Not true for inorganic compounds such as minerals due to defects

• Usually true for molecular compounds, though

Atomic number

# protons

Mass number

# protons and neutrons

Atomic mass

Sum of protons and nuetrons

Isotopes

Same # protons, diff # neutrons

Natural abundance

Percentage of an isotope as represented in nature

Average atomic mass

Weighted average of isotopes accounting for natural abundance

Electronegativity

The ability for an atom to attract electrons toward themselves and repel from other atoms

Bond types

Difference in electronegativity between two elements

• 0: non-polar covalent)

• 0-2: polar covalent

• 2-3 gray area

• above 3: ionic

Molecular compounds have _ bonds

Covalent

Ionic compounds have _ structure

Lattice

Oxidation numbers

• Zero for element in natural state

• +1 group 1

• +2 group 2

• Monatomic ions sum to charge

• Floride -1

• Hydrogen +1 except in metals

• Oxygen -2 except in H2O2 and OF