trial - chem quest

How to calculate atomic mass

the # of protons + # of neutrons = atomic mass (amu)

Why decimal places?

Atomic mass of a single atom is a whole number; Element masses are based on Carbon-12 = 12 amu; Hydrogen (1 amu) is 1/12 the mass of carbon

What is an isotope

A version of an element with the same protons but different neutrons (unique mass)

Isotopes

Most elements have at least two isotopes

Relative abundance

Isotopes exist in nature in different amounts

Trace

An isotope present in very small amounts

Calculating weighted average

Weighted average = (mass × abundance) for all isotopes ÷ 100

Steps of calculating weighted average

Set up equation with subscripts → Sub values → Solve with units

Radioisotopes

A radioactive isotope

Properties of radioisotopes

Unstable nucleus; Can occur naturally or be made artificially; Decay releases radiation

Atomic radius

Distance from nucleus to valence shell

Nuclear charge

the # of protons = positive charge; More protons = stronger pull on electrons

Electron shells

Electrons exist only in allowed shells/energy levels; More shells = valence electrons farther from nucleus

Shielding

Inner electrons block (shield) the nucleus’s pull on valence electrons

Electron-electron repulsion

Electrons repel each other in the same shell; Proton increase usually outweighs repulsion

TIPT - across a period

More protons in nucleus; Shells and shielding constant; Atomic radius decreases

TIPT - down a group

Despite more protons in nucleus; More shells and shielding; Atomic radius increases

What is a trend in the periodic table

A general pattern in properties, with exceptions

Ionic radius

Distance from nucleus to valence shell in ions; Metals form cations; Non-metals form anions

Ionic radius in metals

Metals lose valence electrons → form cations

Ionic radius in non-metals

Non-metals gain electrons → form anions; Same protons, shells, and shielding; More electrons = more repulsion, weaker nuclear pull

Cation and anion size

Cations smaller than parent atoms (fewer shells, less shielding); Anions larger than parent atoms; Cations smaller than most anions

Ionic radius - trends across a period

Cations: radius decreases → same shell, same shielding, more protons → stronger pull; Cations are often isoelectronic; Anions: radius decreases → same shell, same shielding, more protons → stronger pull; Anions are also isoelectronic

Electron affinity

Measure of attraction for an added electron

Nuclear charge - electron affinity

More protons = stronger attraction for added electron

Electron shell/shielding - electron affinity

More shells/shielding = weaker attraction

Electron affinity across a period

More protons = stronger attraction; Shells and shielding constant; Stronger attraction to incoming electrons

First ionization energy

Energy to remove one electron from valence shell of a neutral atom

Nuclear charge - first ionization energy

More protons = stronger pull on valence electrons → more energy needed

Electron shells/shielding - first ionization energy

More shells = valence farther from nucleus; Greater distance + shielding = weaker attraction → less energy needed

FIE - across a period

Increases across a period; More protons = stronger pull; Shells/shielding constant; Harder to remove electron

FIE - down a group

Decreases down a group; More shells + shielding → valence farther from nucleus; Weaker pull → easier to remove; Despite more protons, shielding dominates

Electronegativity

Atom’s ability to attract shared electrons in a covalent bond; Relative measurement (compared to other elements); Determines bond type: pure covalent, polar covalent, ionic; Greater nuclear pull = greater electronegativity

Factors affecting electronegativity

Nuclear charge, electron shells/shielding

Electronegativity - across a period

Increases across a period; More protons = stronger pull on shared electrons; Shells/shielding constant

Electronegativity - down a group

Decreases down a group; Despite more protons, more shells + shielding reduce pull on shared electrons