Chapter 7 Ionic and Metallic Bonding Section 7.1 Ions 1 - - PowerPoint PPT Presentation
Chapter 7 Ionic and Metallic Bonding Section 7.1 Ions 1 Electrons in the highest occupied energy level of an elements atoms are called Valence electrons. To find the number of valence electrons in an atom of a representative element,
Chapter 7 Ionic and Metallic Bonding Section 7.1 Ions
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Electrons in the highest occupied energy level of an element’s atoms are called Valence electrons. To find the number of valence electrons in an atom of a representative element, simply look at its group number. Each noble gas (except He) has eight electrons in its highest energy level.
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Valence Electrons
The noble gases, Group 8, are the only exceptions to the group-number rule. Helium has two valence electrons, and all of the other noble gases have eight. valence electrons are usually the only electrons used in chemical bonds. As a general rule, only the valence electrons are shown in electron dot structures. Electron dot structures are diagrams that show valence electrons as dots. 3
Electron dot structure are diagrams that show valence electrons as dots.
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Electron Dot Diagrams
A way of keeping track of valence electrons. How to write them
Write the symbol Put one dot for each valence electron Don’t pair up until they have to
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The Electron Dot diagram for Nitrogen
electrons.
time to each side.
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Write the electron dot diagram for:
Na Mg C O
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F Ne He
Electron Configurations for Cations
Metals lose electrons to attain noble gas
configuration.
They make positive ions. Na 1s22s22p63s1 - 1 valence electron
Na+ 1s22s22p6 - noble gas configuration
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Electron Dots For Cations, e.g. Calcium
Metals will have few valence electrons
9 Ca
Metals will have few valence electrons These will come off
10 Ca
Electron Dots For Cations, e.g. Calcium
Metals will have few valence electrons These will come off Forming positive ions
11 Ca2+
Electron Dots For Cations, e.g. Calcium
Electron Configurations for Anions
Nonmetals gain electrons to attain noble gas
configuration.
They make negative ions. S 1s22s22p63s23p4 - 6 valence electrons
S2- 1s22s22p63s23p6 - noble gas configuration.
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Electron Dots For Anions, e.g. Phosphorus
Nonmetals will have many valence electrons. They will gain electrons to fill the highest level.
13 P
Practice
Use electron dot diagrams to show how the following form ions
Al Cl C
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Stable Electron Configurations
All atoms react to achieve noble gas
configuration
Noble gases have 2 s and 6 p electrons. 8 valence electrons Also called the octet rule
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Octet Rule
In forming compounds, atoms tend to achieve the electron configuration of a noble gas.
An atom’s loss of valence electrons produces a cation,
Atoms of metals tend to lose their valence electrons, leaving a complete octet in the next-lowest energy level. Atoms of non metals tend to gain electrons or to share electrons with another nonmetal to achieve a complete
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Some ions formed by transition metals do not have noble-gas electron configurations, but have pseudo noble-gas electron configurations. For example, Silver (Ag) forms a pseudo noble-gas electron configuration. (4s24p64d10) The gain of negatively charged electrons by a neutral atom produces an anion.
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Names of ions
Cations keep the name of the metal
–
Ca calcium
–
Ca2+ calcium ion
Anions change ending to – ide – Cl Chlorine
– O Oxygen -
O2- oxide ion
– N Nitrogen
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Formation of Anions
20 Halide ions – the ions that are produced when atom
All halogen atoms have seven valence electrons and need to gain only one electron to achieve the electron configuration of a noble gas. All halide ions (F-, Cl-, Br-, and I-) have charge of 1-.
Questions
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electrons in an atom of a representative element? Look up the group number of that element
Atoms of which elements tend to lose electrons? Nonmetals – gain metals - lose
Cation – atom loses valence electrons Anion – atom gains valence electrons
Section 7.2 Ions Bonds and Ionic Compounds
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Ionic Bonding
Anions and cations are held together by
This is the bond Ionic compounds are called salts. Simplest ratio is called the formula unit. The bond is formed through the transfer of
electrons.
Electrons are transferred to achieve noble gas
configuration.
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Ionic Bonding
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Na Cl
1+ 1-
Ionic Bonding
All the electrons must be accounted for!
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Ionic Bonding
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Ionic Bonding
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Ionic Bonding
3-
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Ionic Bonding
3-
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Ionic Bonding
3-
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Ionic Bonding
3-
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Ionic Bonding
3-
3-
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Ionic Bonding
Formula Unit
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Practice
Use electron dot diagrams to show how the
following elements make an ionic compound and write the formula unit and name the compound.
Mg and Cl
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Practice
Na and N
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Practice
Al and O
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Ionic Compounds
Made up of
– a positive and negative ion – a cation and an anion – a metal and a nonmetal
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Properties of Ionic Compounds
Crystalline structure. A regular repeating arrangement of ions in the
solid.
Ions are strongly bonded. Structure is rigid. High melting points - because of strong forces
between ions.
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Go to page: 197
Compounds composed of cations and anions are called ionic compounds. Although they are composed of ions, ionic compounds are electrically neutral. The electrostatic forces that hold ions together in ionic compounds are called ionic bonds. Ionic compounds can conduct electric current when melted or dissolved in water, because ions are free to move in the solution.
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Go to page: 198
Solve #12, page:196
Classwork
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Solve #18 & 20, page:199
Section 7.3 Metallic Bonding
Metallic Bonds & Properties
Metals are made up of closely packed cations rather than neutral atoms. The valence electrons of metal atoms can be modeled as a sea
Metallic bonds consists of the attraction of the free-floating valence electrons from the positively charged metal ion. The sea-of-electrons model explains many physical properties of metals.
– Good conductors of electrical current because electrons can
flow freely.
– Ductile – they can be drawn into wires. – Malleable – they can be hammered or forced into shapes.
Go to page: 201
Crystalline Structure of Metals
The crystalline structures of metals can be compared to the stacking of
space. Metals are crystalline and they are arranged in very compact and orderly patterns.
There are several closely packed arrangements that are possible.
Body-centered cubic Every atom (except those on the Surface) has eight neighbors.
Go to page: 202
Crystalline Structure of Metals
Face-centered cubic arrangement every atom has twelve neighbors
Hexagonal close-packed arrangement every atom also have twelve neighbors. Because of the hexagonal shape, the pattern is different from the face-centered.
Alloys
Very few of the metallic items that you use every day are pure metals. e.g: spoons. Most of the metals you encounter are alloys Alloys are mixtures composed of two or more elements., at least one of which is a metal. The most important alloys today are steels (Fe & C) e.g: Brass (Cu & Zn) Stainless steel (Fe, Cr, C, & Ni) Alloys properties are often superior to those of their component elements. Sterling silver (92.5% silver & 7.5% copper) is harder and more durable than pure silver, but still soft enough to be made into jewelry and tableware.
Bronze – 7 parts copper to 1 part tin. Bronze is harder than copper and more easily cast. Nonferrous (non-iron) alloys are commonly used to make coins. The most important alloys today are steels. Alloys can form from their component atoms in different ways. If the atoms of the components in an alloy are about the same size, they can replace each
If the atomic sizes are different, the smaller atoms can fit into the spaces between the larger atoms. (interstitial alloy)
Alloys
Questions
metal atoms? Metal cations surrounded by a sea of mobile valence electrons.
metals? Atoms in metals are arranged in a compact and
Their properties are often superior to their component elements.
End of Chapter 7