Valence Electrons, Bohr Diagrams, & Light

Review: Atomic Structure Atoms have a nucleus that contains Protons and Neutrons Electrons are contained in shells that surround the nucleus An atom is made of mostly empty space Protons have a positive charge Electrons have a negative charge Neutrons are Neutral

Review: Electrons & Shells Each electron shell can hold a certain number of electrons Electron shells are filled from the inside out Noble Gases have full outer electron shells All other elements have partially filled outer electron shells Electron Shell Number of Electrons 1 2 8 3 4 18 5 6 32 7

Valence Electrons The electrons in the outer most electron shell are called valence electrons The shell containing electrons that is furthest from the nucleus is called the valence shell The number of electron shells with electrons is the same as the period (row) number The number of valence electrons is the same as the family (column) number

Valence Electrons in Each Family/Group

Noble Gas Stability Noble gases (column all the way to the right) are usually unreactive This is because they have full valence shells (a stable octet) An element with a full valence shell is a happy element  All elements are trying to get a stable octet!

Noble Gas Stability Atoms want to gain stability Atoms will try to gain or lose electrons to have a full valence shell Metals try to lose electrons Non-Metals try to gain electrons

Bohr Models Niels Bohr created a visual model of the atom to make them easy to understand A Bohr Model contains a central nucleus surrounded by electron shells For each model you state the number of protons and neutrons in the nucleus and draw a dot on the electron shells for each electron To determine the number of valence electrons an element has, you look at the number of electrons in the outermost shell

Complete the Bohr Model of the Atom – Arranging Electrons in Energy Levels in your Notebook. For the second half when you are coloring the electrons, remember, you won’t use every circle on every shell – it depends on how many electrons the element has. For example, Sodium has 11 electrons, so you will only use 11 circles.

The closer an electron is to a proton, the more stable the atom! The most stable location for an electron is as close to the nucleus as it can get… that is its ground state configuration (the lowest possible energy level the electron can be at) But electrons can jump from energy level to energy level! An atom is said to be in an excited state when its electrons are at an energy level higher than the ground state.

Electrons absorb or emit energy when they jump from one energy level to another. A quantum of energy is the amount of energy required to move an electron from one energy level to another.

How do we determine (calculate) energy? A scientist (Max Planck) determined hot objects emit energy in packets called “quanta” “quantum” - minimum energy that can be gained or lost by an atom E = h Where E = energy, h = Planck’s constant (6.626 x 10-34 Js), and  = frequency (in s-1)

Photons are bundles of light energy that is emitted by electrons as they go from higher energy levels to lower levels.

High Freq Electromagnetic Spectrum Low Freq High E Low E Light emitted produces a unique emission spectrum.

Wavelength & Frequency Speed of light (c) = 3.00 x 108 m/s Wavelength ( ) = distance between waves Frequency () = # waves that pass point in given time c =   as  increases,  decreases as  increases,  decreases (slinky analogy)

Emission Spectra White light - continuous spectrum Hydrogen atoms - line-emission spectrum Big Question - Why did hydrogen atoms only give off specific frequency (colors) of light?

The “Fingerprints” of Atoms

The atom is quantized, i.e. only certain energies are allowed. Atomic Spectra The atom is quantized, i.e. only certain energies are allowed.

Neils Bohr Solved the Mystery Electron circled nucleus in “orbit” of fixed energy Absorption-electrons can “hop” from ground state to excited state Emission-when electrons “fall” from excited state to ground state Energy difference corresponds to hydrogen’s spectral lines

Complete the Electron Energy and Light POGIL Packet