Octet rule: atoms tend to gain, lose or share electrons so as to have eight electrons in their outer electron shell

Transcription

1 Forma&on of Ions

2 Forma&on of Ions Elements tend to lose or gain electrons to fill their outermost energy levels with eight electrons depending on their electron affinity As a general rule, metals will give electrons away and nonmetals will accept electrons.

3 Octet rule: atoms tend to gain, lose or share electrons so as to have eight electrons in their outer electron shell AAain Noble Gas Status Sodium: 1s 2 2s 2 2p 6 3s 1 [Ne] 3s 1 Chlorine: 1s 2 2s 2 2p 6 3s 2 3P 5 [Ne] 3s 2 3P 5

4 Forma&on of Ions Causes an imbalance of charge (more or less electrons than protons) This imbalance in the element is called ionizing, and the element is transformed into an ion

5 Forma&on of Ions The charge of an ion can be computed by subtrac&ng the number of protons by the new number of electrons: Chlorine would gain 1 electrons so: n = - 1 charge

6 Forma&on of Ions Sodium would lose 1 electrons so: n = +1 An ion and its charge is represented by the element's symbol and then the charge is wriaen azer it as a superscript: Na +1 Cl -1

7 Forma&on of Ions The general term for a posi&ve ion is a ca#on. The general term for a nega&ve ion is an anion.

8 Forma&on of Ions Remembering the Periodic Law will help you realize that all of the elements in each column will have the same charge as an ion:

9 Forma&on of Ions Na = Na +1 K = K +1 Li = Li +1 and so on

10 Forma&on of Ions Unfortunately, since the transi&on metals have only two electrons in their outermost energy level, we cannot use the Rule of Eight to determine their ionic charge.

11 Forma&on of Ions To accommodate this, we will assume that an ion of a transi&on metal will be +2 unless otherwise stated (they have the ability to have more than one oxida&on number).

12 Ionic Compounds

13 Ionic Compounds Ionic compounds are made up by the chemical combination of metallic and non-metallic elements. Most rocks, minerals and gemstones are ionic compounds. Ceramics, bricks and kitchen crockery are made from clays which contain ionic compounds. While most of the above are made up of mixtures of different ionic compounds table salt is a pure ionic compound made up of sodium chloride (NaCl)

14 Proper&es of Ionic Compounds Think of the properties of rocks, bricks, crockery and table salt. What properties do they share? Have high melting and boiling temperatures. Are hard but brittle They also: Do NOT conduct electricity in the solid state They will only conduct electricity if they are melted or dissolved in water

15 Structure of ionic compounds The physical properties of ionic compounds are very different from metals. The structure of ionic compounds must therefore be very different from those present in metals. What do we already know about ionic compounds.

16 What do the proper&es tell us?

17 Structure From the properties we can conclude: The forces between the particles are strong. There are no free-moving electrons present, unlike in metals. There are charged particles present, but in solid state they are not free to move. When an ionic compound melts, however, the particles are free to move and the compound will conduct electricity.

18 The ionic bonding model Metal atoms lose electrons to non- metallic atoms and become posi&vely charged metal ions. Non- metal atoms gain electrons from the metal atoms and so become nega&vely charged non- metal ions. Large numbers of posi&ve and nega&ve ions formed in this way then combine to form a three- dimensional ladce. The three dimensional ladce is held together strongly by electrosta&c forces of aarac&on between posi&ve and nega&ve ions. This electrosta&c force is called ionic bonding.

19 How many chlorine ions surround each sodium ion and vice versa?

20 Using the ionic bonding model to explain the proper&es of sodium chloride

21 High Mel&ng Temperature Ever no&ced that when you eat french fries the food may be hot but the salt does not melt. This is because to melt and ionic solid energy must be provided to allow the ions to break free and move. NaCl has a high mel&ng temp, this indicates a large amount of energy is needed to reduce the electrosta&c aarac&on between the oppositely charged ions and allow them to move freely.

22 Hardness and BriAleness Unlike metals ionic compounds are not malleable. They break when beaten. A force can disrupt the strong electrostatic forces holding the lattice in place. A sodium chloride crystal cannot be scratched easily but if a strong force (a hammer blow) is applied it will shatter. This is because the layers of ions will move relative to each other due to the force. During this movement, ions of like charge will become adjacent to each other. Resulting in repulsion

23 Hardness and BriAleness Figure 6.4 The repulsion between like charges causes this sodium chloride crystal to shatter when it is hit sharply.

24 Electrical Conduc&vity In the solid form, ions in sodium chloride are held in the crystal lattice and are not free to move so cannot conduct electricity. When the solid melts the ions are free to move. The movement of these charged particles to an electrode completes an electrical circuit. In a similar way, when sodium chloride dissolves in water, the ions separate and are free to move towards the opposite charge.

25 Reac&ons of metals with non- metals Metallic atoms have low ionization energies and low electronegativities. Non-metallic atoms have high ionization energies and low electronegativities. In other words metallic atoms lose electrons easily and non-metallic atoms gain electrons easily.

26 Ionic Compounds So the metal atoms lose an electron to the non-metal atoms. In doing so, both atoms will often achieve the electronic configuration of the nearest noblest gas, which is particularly stable.

27 Sodium Chloride When sodium reacts with chlorine: Na atom (1s 2 2s 2 2p 6 3s 1 ) loses an electron to become 1s 2 2s 2 2p 6 (the same as Neon) Cl atom (1s 2 2s 2 2p 6 3s 1 3p 5 ) gains an electron to become 1s 2 2s 2 2p 6 3s 1 3p 6 (the same as argon)

28 Magnesium Oxide What are the electron configurations for Magnesium and Oxygen? How many electrons does magnesium need to lose to get a full outer shell? How many electrons does oxygen need to gain to get a full outer shell? Draw an electron transfer diagram. What is the electrovalency of a magnesium ion and an oxide ion?

29 Magnesium Chloride What are the electron configurations for Mg and Cl? So a Mg atom will have a stable outer shell if 2 electrons are removed. A Cl atom only needs to gain one electron. So how can this work?

30 Chemical Formulas Almost every compound in which a metal is combined with a non-metal displays ionic bonding. The formulas of simple ionic compounds, such as NaCl and MgCl 2 can be predicted from the electron configurations of the atoms.

31 Wri&ng Formulas: Rules Chemical formulas are part of the language of chemists. To understand and use this language, you need to follow a number of fules.

32 Wri&ng Formulas: Rules Simple Ions The posi&ve ion is place first in the formula, the nega&ve ion is second. For example: KF, CuO Posi&ve and nega&ve ions are combined so that the total number of posi&ve charges is balanced by the total number of nega&ve charges. For example, CuS, CuCl 2, AlCl 3 and Al 2 O 3 When there are two or more of a par&cular ion in a compound, then in the chemical formula the number is wriaen as a subscript azer the chemical symbol. For example, Al 2 O 3

33 Polyatomic ions Some ions contain more than one atom. These are called polyatomic ions. nitrate (NO 3- ) and hydroxide (OH - ). If more than one of these ions is used to balance the charge of a compound, then it is placed in brackets with the required number written as a subscript after the brackets. For example Mg(NO 3 ) 2 and Al(OH) 3 Brackets are not required for the formula of sodium nitrate NaNO 3, where there is only one nitrate ion present for each sodium ion.

34 Different Electrovalencies Some elements form ions with different charges. Iron ions can have a charge of +2 or +3. In this situation you need to specify the electrovalency when naming the compound. This is done by placing a Roman numeral representing the electrovalency of the ion immediately after the metal in the name of the compound. For example Iron(II) chloride contains Fe 2+ ions and so the formula is FeCl 2 Iron(III) chloride contains Fe 3+ ions and so the forumla is FeCl 3

35 Metallic Bonds

36 Ca&ons packed in a sea of electrons

37 Metals Metals consist of closely packed cations floating in a sea of electrons. Delocalized electrons All of the atoms are able to share the electrons. The electrons are not bound to individual atoms.

38 Proper&es of Metals Good conductors Ductile Malleable Electrons act as a lubricant, allowing cations to move past each other

39 Metals have a Crystalline Structure Packed spheres of the same size and shape: Body Centered Cubic Face Centered Cubic Hexagonal Close Packed

40 Chromium Body Centered Cubic

41 Gold Face- Centered Cubic

42 Hexagonal Close- Packed Zinc

43 Alloys Mixtures of two or more elements, at least one of which is a metal. Made by melting, mixing, then cooling the metals. May contain non-metals like carbon.

44 Alloys Properties are superior to their components. Sterling silver 92.5% Ag, 7.5% Cu Harder than silver Bronze 7:1 Cu to Sn (tin)

45 Alloys Stainless Steel Fe 80.6%, Cr 18%, C 0.4%, Ni 1% Cast Iron -Fe 96%, C 4%

46 Types of Alloys Two types of formation: Substitutional alloys Similar size atoms replacement Interstitial alloys Different size atoms smaller ions fill interstices (spaces between atoms)