SUBATOMIC PARTICLESSUBATOMIC PARTICLES

ParticleParticle ChargeCharge MassMass LocationLocation

ProtonProton +1+1 1 amu1 amu NucleusNucleus

NeutronNeutron 00 1 amu1 amu NucleusNucleus

ElectronElectron -1-1 1/1836 or 1/1836 or 0 amu 0 amu

Outside Outside NucleusNucleus

Rutherford’s Gold Foil Rutherford’s Gold Foil ExperimentExperiment

Most alpha particles Most alpha particles went straight throughwent straight through

Some of the particles Some of the particles deflected back to the deflected back to the source.source.

Conclusion:Conclusion:

1.1. Atom made up mostly Atom made up mostly of empty space.of empty space.

2.2. Nucleus has an overall Nucleus has an overall positive charge. positive charge.

Bohr’s “Planetary” Atom ModelBohr’s “Planetary” Atom Model

Wave-Mechanical ModelWave-Mechanical Model

Orbit vs. OrbitalOrbit vs. Orbital An orbit describes a particular path that an An orbit describes a particular path that an

object follows as it travels around another object follows as it travels around another objectobject

For example, the moon has an orbit about For example, the moon has an orbit about the earththe earth

Electrons do not follow a particular path Electrons do not follow a particular path around the nucleusaround the nucleus

Instead, an orbital describes the areas Instead, an orbital describes the areas around the nucleus where an electron is around the nucleus where an electron is most likely to be found (probability of most likely to be found (probability of location)location)

The exact path of an electron in this area is The exact path of an electron in this area is not knownnot known

ISOTOPESISOTOPES

Atoms of the same element that have Atoms of the same element that have different numbers of neutrons. different numbers of neutrons.

There are two methods of identifying There are two methods of identifying isotopes. 1. Write mass number with a isotopes. 1. Write mass number with a hyphen after the name of the element, ex: hyphen after the name of the element, ex: Helium-3 or Helium-4, and 2. using the Helium-3 or Helium-4, and 2. using the composition of the nucleus as the isotopes composition of the nucleus as the isotopes nuclear symbol, ex. nuclear symbol, ex. 33He or He or 44He (the He (the number of the bottom left would represent number of the bottom left would represent the atomic number which is the number of the atomic number which is the number of protons, and therefore never changes.protons, and therefore never changes.

Atomic MassAtomic Mass

The average of all the The average of all the naturally naturally occurring isotopes of an element.occurring isotopes of an element.

MUST know how to calculate it!!!!MUST know how to calculate it!!!!

Ex: Naturally occurring chlorine is 75.78% Ex: Naturally occurring chlorine is 75.78% 3535Cl, which has an atomic mass of 34.969 amu, Cl, which has an atomic mass of 34.969 amu, and 24.22% and 24.22% 3737Cl, which has an atomic mass of Cl, which has an atomic mass of 36.966 amu. Calculate the average atomic 36.966 amu. Calculate the average atomic mass (that is, the atomic weight) of chlorine.mass (that is, the atomic weight) of chlorine.

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FIRST PRINCIPLE ENERGY LEVEL:FIRST PRINCIPLE ENERGY LEVEL: holds holds only 2 electrons.only 2 electrons.

SECOND PRINCIPLE ENERGY LEVEL:SECOND PRINCIPLE ENERGY LEVEL: holds only 8 electrons.holds only 8 electrons.

THIRD PRINCIPLE ENERGY LEVEL:THIRD PRINCIPLE ENERGY LEVEL: holds only 18 electrons.holds only 18 electrons.

FOURTH PRINCIPLE ENEGY LEVEL:FOURTH PRINCIPLE ENEGY LEVEL: holds only 32 electrons. holds only 32 electrons.

Valence Electrons - Valence Electrons - The number of electrons in The number of electrons in the last principle energy level. According to the the last principle energy level. According to the octet ruleoctet rule, there can be no more than 8 valence , there can be no more than 8 valence electrons. These electrons affect chemical electrons. These electrons affect chemical properties of the element. properties of the element.

Non-Valence Electrons - Non-Valence Electrons - All other electrons in All other electrons in an atom other than the last level (valence)an atom other than the last level (valence)

Ground vs. Excited Ground vs. Excited StatesStates

In this class we will be performing an experiment In this class we will be performing an experiment called the “Flame Test”. We will be heating up called the “Flame Test”. We will be heating up metal powders in order to excite the electrons to metal powders in order to excite the electrons to jump from a lower energy level to a higher jump from a lower energy level to a higher energy level. energy level.

When an electron returns When an electron returns from a higher energy from a higher energy state to a lower energy statestate to a lower energy state, , it emitsit emits a a specific amount of energy usually in the form of specific amount of energy usually in the form of lightlight. This is known as a . This is known as a bright line spectrumbright line spectrum, and , and can be used to can be used to identifyidentify an element like a an element like a fingerprint.fingerprint.

Bright Line SpectrumBright Line Spectrum

While this light appears as one color to our While this light appears as one color to our eyes, it is actually composed of many eyes, it is actually composed of many different wavelengths each of which can different wavelengths each of which can be seen using a be seen using a spectroscopespectroscope

The energy that is given off when an The energy that is given off when an excited electron falls to the ground state is excited electron falls to the ground state is separated into its component separated into its component wavelengths.wavelengths.

IonsIons

An atom with a charge.An atom with a charge.

We can never change the number We can never change the number of protons!of protons! So to produce a charge So to produce a charge we can add or subtract electronswe can add or subtract electrons

Atoms lose or gain electrons in order to Atoms lose or gain electrons in order to have a complete outer shell (to have a complete outer shell (to become more stable), and follow the become more stable), and follow the octet rule.octet rule.

Lewis Dot DiagramsLewis Dot Diagrams Helps to show the number of valence electrons in the last Helps to show the number of valence electrons in the last

principle energy level. There can only be 2 electrons on principle energy level. There can only be 2 electrons on each side of the symbol of the element. each side of the symbol of the element.

1.1. Put the 1st and 2nd valence electrons on any side of X.Put the 1st and 2nd valence electrons on any side of X.2.2. For the 3rd, 4th, and 5th electrons, put each electron For the 3rd, 4th, and 5th electrons, put each electron

on a different side of the symbol.on a different side of the symbol.3.3. For the 6th, 7th and 8th electrons, add them to any For the 6th, 7th and 8th electrons, add them to any

side with 1 electron. side with 1 electron.