Valence Electrons

Periods: Energy Levels (n) Each row in the periodic table is called a “period” The period corresponds to a specific energy level of the atom The top row, Period 1, is closest to the nucleus, the next one down is Period 2, etc…until you end with Period 7. Level 1: s Levels 2 and 3: s,p Levels 4 and 5: s,p,d Levels 6 and 7: s,p,d,f

Groups: Valence Electrons Each column in the Periodic Table is called a “group” Each element in a group has the same number of electrons in their outer energy level (the valence level). The electrons in the outer shell are called “Valence Electrons” Red: Group 1 Orange: Group 2 Yellow: Group 13 Green: Group 1 Sky Blue: Group 15 Baby Blue: Group 16 Dark Blue: Group 17 Purple: Group 18

Valence Electrons Valence electrons are the electrons in the highest occupied energy level of the atom. Valence electrons are the only electrons generally involved in bond formation (which we will talk about in the next unit!)

Bohr Atomic Structures Electron Configuration of Na: 1s22s22p63s1 The first energy level contains 2 electrons. (s orbital…1s2) The second level contains 8 electrons. (2s and 2p orbitals…2s22p6) How many electrons do you see in the outermost level? 3s1… 1electron! This is the Valence number. Sodium has 1 Valence electron.

Electron Dot Structure: Lewis Dot Diagrams A notation showing the valence electrons surrounding the atomic symbol. How many valence electrons in Cl? C?

Lewis Dot Structures Find out which group (column) your element is in. This will tell you the number of valence electrons your element has. You will only draw the valence electrons.

C Lewis Structures 1)Write the element symbol. 2) Carbon is in the 4th group, so it has 4 valence electrons. 3) Starting at either the right or left of the element symbol, draw 4 electrons, (dots), around the element symbol. C

The History of the Periodic Table and Trends

In the old days… Many elements were known in the ancient world- copper, gold, silver, lead, etc. For several hundred years, elements were discovered by alchemists Alchemy was the ultimate search for wisdom and immortality.

By 1860, more than 60 elements had been discovered….HOWEVER, There was no consistent organization of the elements. No one was using the same method to determine mass of atoms, or the ratios of atoms in compounds In 1860, Stanislao Cannizzaro of Italy presented a convincing method to measure the mass of atoms, thus creating standard values for atomic mass. Now that there are some common standards…

The Matter of Mendeleev In 1869, Dmitri Mendeleev began to try to arrange the elements. Inspired by solitaire, he started to find patterns in the properties of elements, and arranged the known elements by atomic mass in a Periodic (repeating) Table.

Mendeleev’s Genius Mendeleev recognized there were undiscovered elements. By using his periodic table, he could predict the chemical properties of the undiscovered elements. Years later, Scandium, Gallium, and Germanium were discovered and were characteristic of the properties Mendeleev predicted! *swoon*

Henry Moseley 1911: Henry Moseley (working under the direction of Rutherford) rearranged the Periodic Table to go horizontally, and put the elements in order by atomic number.

Variations on the Periodic Table The Mayan Periodic Table of Elements by Mitch Fincher A Spiral Periodic Table by Prof. Thoedor Benfey

The future of the periodic table?

Periodic Trends Now that the periodic table is organized, what patterns can we find? What does it even mean to be “periodic”?

Thanks, to Moseley, we learn that patterns arise because of PROTONS!!! This led to the development of the Periodic Law: the physical & chemical properties of the elements are periodic functions of their atomic numbers. ** In other words, when the elements are arranged in order of increasing atomic number, elements with similar properties appear at regular intervals.

Pattern: Families Elements in column share similar traits, and are called families: These columns are also called groups.

The Alkali Metals 1 valence electron Highly reactive with water Form ionic compounds Do not occur in nature as pure elements (always in compounds)

Alkaline-Earth Metals Have 2 valence electrons Reactive, but less reactive than alkali metals Are ductile, malleable and have a silvery luster Form alkaline (basic) solutions) when put in water

Transition metals… and inner transition metals Are less reactive than groups 1 and 2. Tend not to react in water. Are malleable and ductile, but still harder than group 1 & 2. Tend to be solids at room temperature. Are good conductors of electricity and heat. **Inner transition metals tend to be radioactive

Nonmetals Poor conductors of heat and electricity Often are found as gases or liquids, sometimes solids.

Halogens Are nonmetals highly reactive with metals- most reactive is fluorine, least reactive is astatine Mostly exist as gases or liquids (except At -solid) Have 7 valence electrons

Noble gases At room temperature, exist as gases. Are completely unreactive Have full s and p orbitals Are odorless, colorless, nonflammable

Metalloids Tend to be solids Have properties similar to both metals and nonmetals Tend to be semiconductors (which means they are useful for technological uses)

Valence Electrons: The outermost s & p electrons

Ions Ionization energy Charged atoms that become charged by losing or gaining electrons Ionization energy Energy necessary to make an ion by removing an electron from a neutral atom

Rule #1 to remember! When an element loses an electron, we can think of it as being given away, which is a good thing or POSITIVE thing to do.

Group 1 Elements H, Li, Na, K, Rb, Cs, Fr Achieve a stable octet (full outer shell) by losing 1 electron, which forms a +1 ion H+ , Li+ , Na+ , etc…

Group 2 Elements Be, Mg, Ca, Sr, Ba, Ra Achieve a stable octet by losing 2 electrons, which forms a +2 ion Be2+, Mg2+, Ca2+, etc…

Rule #2 to remember! When an element gains an electron, we can think of it as it is being stolen from another ion, which is a bad or NEGATIVE thing to do.

Group 7 Elements F, Cl, Br, I, At Achieve a stable octet by stealing (gaining) 1 electron, which forms a -1 ion F-, Cl-, Br- , etc…

Group 6 Elements O, S, Se, Te, Po Achieve a stable octet by stealing (gaining) 2 electrons, which forms a 2- ion O2- , S2- , Se2-, etc…