Atomic Structure and Periodic

TrendsGabrielle GarciaEmily Surgeon

Valence Electrons & Electron

Arrangement Valence Electrons equal to group #

Ex. How many valence electrons are in P?

Answer: 5

Electron arrangement: The way in which the shells of an atom are filled up/ arranged with electrons

1st shell: 2; 2nd: 8; 3rd: 8

Highest IB test will ask is Ca: 2,8,8,2

Ex. What is the electron arrangement of Si?

Answer: 2, 8, 4

Atomic #, Mass #, & Isotopes

Atomic #: Number of protons/electrons in an atom

Mass #: Number of neutrons in an atom

Isotope: atoms that can have different mass # but same atomic #

Chemical properties of isotopes are the samePhysical properties are not

Ex. What is the most common isotope of Nitrogen?Answer: N 14

Calculating Average Atomic

MassAverage Atomic Mass:

%(mass1)+%(mass2)+...Ex. Carbon(12.000000) (0.9890) + (13.003355) (0.0110) = 12.011 amu

Mass Spectrometer

1: Vaporization- element is heated until it’ s a gas

2: Ionization- electrons are knocked off and it is turned into a positive ion

3: Electric field- positive and negative, accelerates and focuses

4: Magnetic field deflects, lightest ones get most deflection

5: Detector- Mass is converted into abundance

Periodic Trends

Ionization EnergyThe tendency of an atom to gain electrons in order to fill a shell

Increases across periods and up groups

Ex. Which has higher ionization energy, Antimony or Nitrogen?

Answer: Nitrogen

Why?

Antimony has more electron shells than Nitrogen, so its outer electron is shielded from the nucleus and experiences lower Zeff (effective nuclear charge) and is held more loosely. Thus, it is easier to remove an electron

Atomic RadiiSize of an atom

Decreases across periods, decreases down groups

Ex. Which has larger atomic radius: Francium or Radium?

Answer: Francium

Why?

Francium has less protons than Radium, but the same number of shells. So its outer electron experiences lower Zeff and is held more loosely. Thus it is a larger atom.

Ionic RadiiSize of an atom’s ion

Decreases across a period, increases down a group

Ex. Which has a larger ionic radius: Sodium or Sulfur?

Answer: Sulfur

Why?

Sodium has lost electrons and now has more protons than electrons, while Sulfur has gained electrons and now has more electrons than protons. So, the outer electrons in Sodium are held tighter by the protons (feels a higher Zeff) and its ion is smaller

ElectronegativityThe tendency for an atom to attract electrons when forming an ionic bond

Increases across a period, increases up a group

Ex. Which has a higher electronegativity: Cesium or Lithium?

Answer: Lithium

Why?

Cesium has more electron shells than Lithium, so its outer electron is shielded from the nucleus (and experiences lower Zeff) and is held more loosely. Thus, it is pulling less on other electrons.

Melting PointTemperature at which a solid element will melt

The stronger the forces that act between molecules of a substance, the higher the melting point tends to be.

Ex. Which has a higher melting point: Carbon or Sodium?

Answer: Carbon