Ions and Valence Electrons

Transcription

1 Ions and Valence Electrons 4/4/16 SLO Students will be able to determine the number of valence electrons of each element and how cations and anions are formed.

2 What do we already know about Ions? Formed by gain or loss of electron Positive ions are called Cations Ex. Ca +2, Li +, Al +3 Negative ions are called Anions Ex. Br -, O -2

3 Ions Continued When positive, the name of the ion is the same as that of the element Ex. K + Potassium, Mg +2 Magnesium When negative, the name of the ion is the root name of the element plus ide Ex. S -2 Sulfide I - Iodide Valence electrons- are the only electrons gained or lost.

4 Review of Valence electrons Valence electrons are the outer shell electrons; Electrons in the highest occupied energy level They determine the chemical properties of an element They are farthest from the nucleus and therefore easiest to remove

5 Valence Electrons For the representative groups 1A-7A and the noble gases, finding the number of valence electrons is easy! Valence electrons are the same as the group number Finding valence electrons for the transition metals requires finding the electron configuration Look at the electrons in the highest principal energy level

6 Stability of atoms Octet Rule- Atoms are stable if they have 8 valence electrons, a noble gas configuration In order to become stable and meet the octet rule, they must gain, lose or share electrons Exceptions for ions: Hydrogen, Beryllium, Lithium, and Helium stable with 2 (full outer shell of electrons)

7 Becoming Stable Atoms of metals tend to lose their valence electrons, leaving a complete octet in the next-lowest energy level. Form Cations Atoms of some non-metals tend to gain electrons or to share electrons with another nonmetal to achieve a complete octet. Form Anions

8 Forming cations The most common cations are those produced by the loss of valence electrons from metal atoms. You can represent the electron loss, or ionization, of the sodium atom by drawing the complete electron configuration of the atom and of the ion formed. Notice just the valence electron is lost..

9 7.1 Formation of Cations The electron configuration of the sodium ion is the same as that of a neon atom.

10 7.1 Valence Electrons Electron dot structures are diagrams that show valence electrons as dots.

11 7.1 Formation of Cations Using electron dot structures, you can show the ionization more simply.

12 7.1 Formation of Cations The sodium atoms in a sodium-vapor lamp ionize to form sodium cations.

13 7.1 Formation of Cations A magnesium atom attains the electron configuration of neon by losing both valence electrons. The loss of valence electrons produces a magnesium cation with a charge of 2+.

14 7.1 Formation of Cations Walnuts are a good dietary source of magnesium. Magnesium ions (Mg 2+ ) aid in digestive processes.

15 7.1 Formation of Cations Cations of Group 1A elements always have a charge of 1+. Cations of group 2A elements always have a charge of 2+.

16 Formation of Anions The gain of negatively charged electrons by a neutral atom produces an anion. An anion is an atom or a group of atoms with a negative charge. The name of an anion typically ends in -ide. Example: oxygen would become oxide Sulfur would become sulfide Chlorine would become chloride

17 7.1 Formation of Anions The figure shows the symbols of anions formed by some elements in Groups 5A, 6A, and 7A.

18 7.1 Formation of Anions A gain of one electron gives chlorine an octet and converts a chlorine atom into a chloride ion. It has the same electron configuration as the noble gas argon.

19 7.1 Formation of Anions Both a chloride ion and the argon atom have an octet of electrons in their highest occupied energy levels.

20 7.1 Formation of Anions In this equation, each dot in the electron dot structure represents an electron in the valence shell in the electron configuration diagram.

21 7.1 Formation of Anions The negatively charged ions in seawater the anions are mostly chloride ions.

22 7.1 Formation of Anions The ions that are produced when atoms of chlorine and other halogens gain electrons are called halide ions. All halogen atoms have seven valence electrons. All halogen atoms need to gain only one electron to achieve the electron configuration of a noble gas.

23 7.1 Formation of Anions Oxygen is in Group 6A and has 6 valence electrons

24 How to predict the charge First remember that an atom is stable with 8 valence electrons Metals tend to lose electrons to get charges of 1+, 2+, and 3+ Nonmetals tend to gain electrons to get charges of 1-, 2-, and 3- The max charge is USUALLY + or - 3

25 Unusual or Multiple charges Lead and Tin both have charges of 2+ or 4+ Iron 3+ or 2+ Copper 1+ or 2+ Manganese 1+, 2+, 5+, 7+ Zinc 2+ only Silver 1+ only Cadmium 2+ only

26 Practice Determine whether the following elements will gain or lose electrons and what the final charge will be: Bromine Phosphorus Neon Cesium Beryllium

27 7.1 Section Quiz. 1. How many valence electrons are there in an atom of oxygen?

28 7.1 Section Quiz. 2. Atoms that tend to gain a noble gas configuration by losing valence electrons are metals. nonmetals. noble gases. representative elements.

29 7.1 Section Quiz. 3. When a magnesium atom forms a cation, it does so by losing two electrons. gaining two electrons. losing one electron. gaining one electron.

30 7.1 Section Quiz. 4. When a bromine atom forms an anion, it does so by losing two electrons. gaining two electrons. losing one electron. gaining one electron

31 Exit Questions What are electron dot structures? What are valence electrons? How can you find the number of valence electrons for the Representative Elements?

32 Classwork Reading Assignment: Sec 7.1 Written Assignment: pg. 199, #1-6

33 Do Now- Complete in your NB How many electrons will each element lose in forming a cation? a. Calcium b. Aluminum c. Cesium Identify the charge of the ion formed when a. A Potassium atom loses one electron. b. A Zinc atom loses two electrons c. A Fluorine atom gains one electron.

34 Homework Check! pg. 199, # The number of valence electrons in a representative element can be determined by looking up the group number. 2. Cations are formed when an atom loses an electron. 3. Anions are formed when an atom gains an electron. 4. Atoms of nonmetallic elements tend to gain electrons and atoms of metallic elements tend to lose electrons. 5. a. 1 b. 4 c. 2 d a. K b. C c. Mg d. O

35 Previous Vocabulary Ion Alkaline Earth Metals Octet Rule Electron Dot Structures Cation Halogens Valence Electron Anion Transition Metals Noble Gases Representative Elements Alkali Metals Inner Transition Metals