Chapter 3 Chapter 3 Atomic Structure Atomic Structure

The Structure Of the AtomThe Structure Of the Atom

ParticleParticle mass mass chargecharge locationlocation

ProtonProton 1 AMU1 AMU +1 +1 in nucleusin nucleus

NeutronNeutron 1 AMU 1 AMU 0 0 in nucleusin nucleus

Electron 0 AMU Electron 0 AMU -1 outside nucleus -1 outside nucleus

Atomic number – number of protons in the Atomic number – number of protons in the nucleus, It determines which element an nucleus, It determines which element an atom is atom is

A neutral atom has the same number A neutral atom has the same number of protons as electronsof protons as electronsExample: atomic # 12 – magnesium has Example: atomic # 12 – magnesium has 12 protons and 12 electrons12 protons and 12 electronsAn atom can gain or lose electrons to An atom can gain or lose electrons to become an ionbecome an ion

Ions have a charge and are very different Ions have a charge and are very different than the atoms that they used to bethan the atoms that they used to be

Na is a very reactive metal. Na is a very reactive metal. http://www5.wittenberg.edu/academics/chem/fac_staff/dmcdowell/alkalishow.html

Na+ ion is part of table salt and is Na+ ion is part of table salt and is necessary for life.necessary for life.

IsotopesIsotopes

Atoms of an element all have the same Atoms of an element all have the same number of protons and electrons; number of protons and electrons; however, they can have different however, they can have different number of neutrons. number of neutrons.

Isotopes – atoms of the same element Isotopes – atoms of the same element that differ in their number of neutrons.that differ in their number of neutrons.

Isotopes of an element have the Isotopes of an element have the samesame chemical properties (differ only in mass).chemical properties (differ only in mass).

Isotopes of HydrogenIsotopes of Hydrogen

Isotopes of CarbonIsotopes of Carbon

Isotopic NotationIsotopic Notation

http://preparatorychemistry.com/Bishop_Isotope_Notation.htm

# of neutrons = mass # - # of protons# of neutrons = mass # - # of protons

1 AMU = exactly 1/12 the mass of one 1 AMU = exactly 1/12 the mass of one atom of C-12atom of C-12

The mass of an element given on the The mass of an element given on the chart is an average of the isotopes of chart is an average of the isotopes of that element found in nature.that element found in nature.

Some isotopes are stable and some are Some isotopes are stable and some are not.not.

If an atom has the wrong number of If an atom has the wrong number of neutrons it will be unstable (see page 113)neutrons it will be unstable (see page 113)

Also, if an atom has too many protons Also, if an atom has too many protons (more than 83) it will be unstable.(more than 83) it will be unstable.

Unstable atoms are radioactive and break Unstable atoms are radioactive and break down (nuclear decay)down (nuclear decay)

They eventually change to a stable They eventually change to a stable elementelement

Stability of IsotopesStability of Isotopes

Half life – the time it takes for one Half life – the time it takes for one half of a sample of a radioactive half of a sample of a radioactive element to change. element to change.

If you start with 4 grams of uranium, after If you start with 4 grams of uranium, after one half-life you will have only 2 grams of one half-life you will have only 2 grams of uranium. The rest will be changed to uranium. The rest will be changed to another element. another element.

If you start with 4 grams of uranium, how If you start with 4 grams of uranium, how much will be left after 4 half lives?much will be left after 4 half lives?

Types of Radioactive DecayTypes of Radioactive Decay

NameName IdentityIdentity Charge PenetrationCharge Penetration

Alpha particle He nucleiAlpha particle He nuclei +2 stopped by paper+2 stopped by paper

Beta particle electronBeta particle electron -1 stopped by clothing-1 stopped by clothing

Gamma ray, high energy light 0 thick lead usedGamma ray, high energy light 0 thick lead used

Nuclear Decay of UraniumNuclear Decay of Uranium

Emitting alpha and gamma particlesEmitting alpha and gamma particles

Decay of I-131Decay of I-131

emitting beta particleemitting beta particle

Decay of Rb-81Decay of Rb-81

Electron captureElectron capture

Assignment: page 122 &123 Assignment: page 122 &123 questions 3-13, 15-21questions 3-13, 15-21