Completing the Model of the Atom Chapter 7 Completing the Model of the Atom

Section 7.1 Present Day Atomic Theory

Present Day Atomic Model In the present day model of the atom, neutrons, and protons form a nucleus at the center of the atom. Negatively charged electrons are distributed in space around the nucleus. Electron with the most energy are farthest from the nucleus in the outermost energy level.

Valence Electrons Electrons in the highest energy level. Their number determines the chemical properties of an atom. Usually the only electrons used in chemical bonds.

Electron Dot Structures Show the valence electrons

Determining Valence Electrons The number of valence electrons corresponds to the group #

Energy Levels The period number on the periodic table represents the outermost energy level in which valence electrons are found. Periods

Lithium Lithium is in Group 1, period 2. It has 1 valence electron in the 2nd energy level.

Check Point Sulfur (#16) How many valence electrons does it have? What energy level are the valence electrons in?

Emission Spectra Each element has its own unique set of spectral lines. The colored lines indicate that electrons are moving from higher energy levels to lower energy levels,releasing energy. The colored lines indicates the amount of energy (in the form of light) that is being released.

Heisenberg Uncertainty Principle In the 1920’s Werner Heisenberg determined that it’s impossible to measure accurately BOTH the position and velocity (speed) of an electron at the same time.

Sublevels Sublevels are divisions within an energy level. The energy sublevels are named s, p, d, f (lowest energy to highest energy) .

Aufbau Principle This principle states that each electron must occupy the lowest energy sublevel first. Example: s,p,d,f (lowest energy to highest energy) An electron will occupy an “s” orbital before it will occupy a “p” orbital.

Orbital An orbital is the space around the nucleus in which there is a high probability of finding an electron. Orbitals have different sizes and shapes.

Pauli Exclusion Principle An orbital (drawn as a square) can hold a maximum of 2 electrons (represented by arrows). The electrons must have opposite spins. Electrons Orbital

Sublevels & Orbitals The “s” sublevel has 1 orbital. Therefore it can hold a maximum of 2 electrons. The “p” sublevel has 3 orbitals. It can hold a maximum of 6 electrons. The “d” sublevel has 5 orbitals. It can hold a maximum of 10 electrons. The “f” sublevel has 7 orbitals. It can hold a maximum of 14 electrons.

Orbitals & Electrons s sublevel p sublevel d sublevel f sublevel Number of orbitals 1 3 5 7 Number of electrons 2 6 10 14

Hund’s Rule All orbitals in a sublevel will receive one electron before a second electron can be added. Analogy: Students could fill each seat of a school bus, one person at a time, before doubling up.

Electron Configuration The way electrons are arranged around the nucleus. This is the most stable arrangement of electrons in sublevels and orbitals.

Section 7.2 The Periodic Table and Atomic Structure

Orbitals and The Periodic Table The position of any element on the periodic table shows which sublevels (s,p,d,f) the valence electrons occupy. The shape of the modern periodic table is a direct result of the order in which electrons fill energy sublevels and their orbitals. The periodic table is divided into blocks that show the sublevels occupied by the electrons.

Blocks in the Periodic Table

Standard Notation for Electron Configuration Number of electrons in the sublevel Energy Level Sublevel www.chemistrygeek.com/chemistrypowerpoin

Electron Configurations & Orbital Diagrams

Check Point Determine the electron configuration for Carbon Neon Calcium

Check Point Determine what elements are denoted by the following electron configurations: 1s22s22p63s23p4 1s22s22p63s23p64s1