Life on the edge Valance electrons

ChemCatalyst The three atoms below have similar reactivity and chemical behavior. Where are these elements located on the periodic table? What do you think might be responsible for their similar properties? (cont.) Unit 1 • Investigation III 2

(cont.) Unit 1 • Investigation III 3

Answer Amount of neutrons, protons and electrons are different Amount of electrons in the outermost ring is the same

The Big Question What accounts for the similar chemistry of elements in the same group? Unit 1 • Investigation III 5

You will be able to: Give the number of valence electrons for an element. Unit 1 • Investigation III 6

Changing… The number of protons, results in a new element The number of neutrons, a more or less stable variation of the same element with different mass (formation of ISOTOPES) The number of electrons…

What Bohr realized That various chemical and physical properties of the elements can be traced to the arrangement of electrons in the orbits (shells).

Activity Purpose: The various physical and chemical properties of the elements can be traced to the electrons. By studying electrons further we may be able to unlock the key to creating substances similar to gold. This lesson will reveal the arrangement of electrons within atoms. Unit 1 • Investigation III 9

Procedure Each student receives a copy of the handout and question worksheet. Work primarily on your own. By using the information on the diagrams, answer the following questions We will review the answers to the first 7 questions as a class, before finishing them out

Question 1 What do the atoms of all of Group 1 elements have in common?

Answer Question 1 A single electron in the outermost shell, orbit or ring

Question 2 How does the number of elements change as you move from atom to atom across a row?

Answer Question 2 The number of electrons in the outermost row increases by 1 as one moves across a row (period)

Question 3 How does the arrangement of electrons change as you move down the columns

Answer to 3 It seems like more rings are added

Question 4 How many shells of electrons does bromine have? How many electrons in bromine’s outermost shell?

Answer to 4 4, 7

Question 5 Predict the number of electrons in iodine’s outermost shell.

Answer to 5 7, same as all other elements in the group

Question 6 What happens to the electron count and the number of shells when you move from Neon (NE) to Sodium (Na)?

Answer to 6 One electron was added to a new ring No room for the electron in the inner rings

Question 7 What group is thallium (Tl) in? How many electrons will it have in its outermost shell?

Answer to 7 Group 13 or 3a 3 electrons

Bohr and numbering shells Bohr proposed that electrons could be found in different shells around the nucleus. The letter “n” is referred to as the quantum number. N also refers the position of the shell relative to the nucleus, with 1 being closest to the nucleus Note the connection between the maximum quantum number and the period value for an element Unit 1 • Investigation III 26

(cont.) (cont.) Unit 1 • Investigation III 27

The outermost shell of each drawing is called the valence shell. (cont.) The outermost shell of each drawing is called the valence shell. The valence shell contains the valence electrons. All other electrons are considered core electrons. Unit 1 • Investigation III 28

Question 8 How many valence electrons does the element Se have? What about Na?

Answer to 8 Selenium has 6 valence electrons, sodium has 1

Question 9 How many valence electrons do the halogens have? How many do the noble gases have

Answer to 9 Halogens have 7 Nobles have 2 or 8

Question 10 How many CORE electrons does potassium (K) have? What about Germanium (Ge)?

Answer to 10 Oxygen and neon have 2 core electrons

Question 11 How many core electrons does oxygen have? What about Neon?

Answer to 11 18- k 28 Ge 28 Br

Question 12 If an atom has four shells containing electrons, what row is it in?

Answer to 12 IVA

Question 13 How many electron shells do you think Rb has? How many electrons will its outermost shell?

Answer to 13 5 shells 1 electron in in its outermost shell

Question 14 He pattern in the chart begins to vary between the element calcium and the element gallium. Explain what you think is going on?

Answer to 14 Have to start taking into account the transition metals

Question 15 Recall the card sort you did for the “Create a table ” lab. How were the valance electrons represented on these cards?

Answer to 15 The number of pegs or sticks attached to the circle

Valance electrons of transition metals The arrangement of the electrons into shells determines the number of valance electrons This gets complicated for the transition metals As we shall soon talk about, each shell can be further divided into sub-shells Specific sub-shells act as locations for valence electrons

Making Sense Explain how you can determine the arrangement of an element’s electrons, from the element’s position on the periodic table. Unit 1 • Investigation III 46

Making Sense Generally arrangement depends on position in periodic table Group determines valence electrons Period determines # of shells/rings

If you finish early Predict the electron arrangement of Scandium. Draw a picture of it. Explain your reasoning

Answer to If you finish early Sc First( innermost shell) 2 2nd 8 3rd (8 +1 = 9) 4th 2

Wrap-Up Electrons occupy different shells around the nucleus of an atom. Each electron shell can hold a specific maximum number of electrons. The valence electrons are in the outermost electron shell of an atom. Electrons that are not valence electrons are called core electrons. (cont.) Unit 1 • Investigation III 50

Elements with the same number of valence electrons have similar chemistry and are in the same group. Unit 1 • Investigation III 51

Max number of electrons in each orbit (shell) 1st : 2 electrons 2nd: 8 electrons 3rd: 18 electrons 4th: 32 electrons

Check in Provide the following information for the element with atomic number 34: The elements name and symbol The number of protons in the nucleus The number of core electrons for this element The number of valence electrons The group number for this element The names of other elements with similar chemical traits and properties