6.1_Introduction to Chemical Bonding.pptx
- 3. How do atoms join together? • A huge variety of substances are possible because atoms join together by forming chemical bonds. • A chemical bond is a mutual electrical attraction between the nuclei and the valence electrons of different atoms that binds the atoms together. • A group of atoms that are held together by chemical bonds is called a molecule. • https://www.youtube.com/watch?v=OTgpN62ou24
- 4. What are valence electrons? • The energy level furthest from the nucleus is called the outermost energy level. • Electrons found in the outermost energy level of an atom are called valence electrons. • https://www.youtube.com/watch?v=x1gdfkvkPTk
- 5. How does the periodic table show the number of valence electrons? • Elements in the same group, or vertical column, have the same number of valence electrons. • You can use the group number to find the number of valence electrons in Groups 1, 2, and 13–18. • There is no simple rule to find the number of valence electrons in Groups 3–12.
- 6. Unit 3 Lesson 3 Electrons and Chemical Bonding
- 7. How does the periodic table show the number of valence electrons? • Determine the number of valence electrons in atoms of carbon (C), nitrogen (N), and fluorine (F).
- 8. Why do atoms form bonds? • An atom tends to form bonds if its outermost energy level is not full with eight electrons (octet rule). • Atoms that have fewer than eight valence electrons, except for helium, do not have a full outermost energy level. • These atoms gain, lose, or share valence electrons to form bonds.
- 9. Why do atoms form bonds? • Forming bonds allows atoms to fill their outermost energy level. • An ion is a charged particle that forms when an atom loses or gains an electron. • The ions formed by chlorine and sodium both have eight valence electrons. Bonds hold the negative and positive ions together, producing sodium chloride. Copyright © Houghton Mifflin Harcourt Publishing Company
- 10. Why do atoms form bonds? Copyright © Houghton Mifflin Harcourt Publishing Company
- 11. What is an ion? • An atom has a neutral charge because it has an equal number of electrons and protons. • An ion is a particle with a positive or negative charge. • An ion forms when an atom gains or loses electrons from its outer, or valence, shell.
- 12. How does an ionic bond form? • An ionic bond a chemical bond that results from the electrical attraction between anions and cations. • Ionic bonds form when electrons are transferred from a metal atom to a nonmetal atom. • In the process of ionic bonding, valence electrons move from the outer shell of the metal atom to the outer shell of the nonmetal atom. Copyright © Houghton Mifflin Harcourt Publishing Company
- 13. How does an ionic bond form? • How are the sodium and chlorine atoms held together in the compound sodium chloride? Na + Cl NaCl sodium loses its one valence electron to form the cation Na+ chlorine gains that electron to form the anion Cl- Na+ is attracted to Cl- (opposites attract) and an ionic bond forms
- 14. What is a covalent bond? • A covalent bond a chemical bond that results from the sharing of electron pairs between two atoms • When two nonmetal atoms bond, a large amount of energy is needed for either atom to lose an electron. So they bond by sharing electrons. • In a covalent bond, the shared electrons fill empty spaces in the outermost electron shell of each atom.
- 15. Copyright © Houghton Mifflin Harcourt Publishing Company What is a covalent bond? • nonpolar covalent bond- a covalent bond in which the bonding electrons are shared equally by the atoms forming the bond -because their electronegativities are essentially equal • polar covalent bond- a covalent bond in which the bonded atoms have an unequal attraction for the shared electrons -because one atom has a greater electronegativity than the other
- 16. What is a covalent bond? https://www.youtube.com/watch?v=lP_EsVY4CVg
- 17. Determining Bond Type • Find the absolute difference in the electronegativities of the bonding atoms. • The greater the difference, the greater the % ionic character which makes it more like an ionic bond. – IF the absolute difference is • < 0.3 the bond is nonpolar covalent • > 0.3 and < 1.7 the bond is polar covalent • > 1.7 the bond is ionic Electronegativity is a measure of an atom’s ability to attract electrons.
- 19. Determining Bond Type Electronegativity of Sulfur is 2.5 Hydrogen: 2.1, Cesium: 0.7, Chlorine 3.0
- 21. 1- Electron pairs are shared in covalent bonds and electrons are transferred between atoms in ionic bonds. 2-The difference in the electronegativities of bonding atoms determines the bond type. For problem #3 use the electronegativity chart on page 161. 3a- Li = 1.0 F = 4.0 4.0-1.0 = 3.0 ionic bond 3b- Cu = 1.9 S = 2.5 2.5-1.9=0.6 polar covalent 3c- I = 2.5 Br = 2.8 2.8-2.5=0.3 polar covalent 4- c (0.3) < b (0.6) < a (3.0)
- 22. What properties do most ionic compounds share? • When ions bond, they form a repeating three- dimensional pattern called a crystal lattice. • Each ion has many oppositely charged ions around it, and every ion is held firmly in place with strong bonds. • It takes a lot of energy to separate these ions from one another. So most ionic compounds have high melting and boiling points.
- 23. What properties do most ionic compounds share? • Sodium chloride consists of sodium and chloride ions held together in a crystal lattice structure.
- 24. What properties do most ionic compounds share? • The crystals of ionic compounds are hard and brittle. • Striking a crystal of an ionic compound with a hammer will likely shatter the crystals in many places.
- 25. What properties do most ionic compounds share? • Solid ionic compounds are poor conductors of electric current, because the ions are held tightly in place. • Melting an ionic solid, however, allows the individual ions to move around. Melted ionic compounds can conduct an electric current. • Ionic compounds dissolved in water can also conduct an electric current.
- 26. What properties do most ionic compounds share? • Solubility is the ability to dissolve in liquid. Most ionic compounds dissolve in water. • When salt is added to water, water molecules attract the positive and negative salt ions. • Water molecules surround each ion, and move the ions apart from each other. The separated ions dissolve in water. Copyright © Houghton Mifflin Harcourt Publishing Company
- 27. What is a molecule? • Substances that have covalent bonds are made of individual particles called molecules. • A molecule is a group of atoms held together by chemical bonds. • A molecule is the smallest unit of a compound that can be identified as that compound.
- 28. What is a molecule? • In a water molecule, two hydrogen atoms form covalent bonds with a central oxygen atom.
- 29. What properties do most covalent compounds share? • Some covalent compounds dissolve in water. Other covalent compounds do not. • Wax molecules have a stronger attraction to other wax molecules than they have to water molecules. This is why wax does not dissolve in water.
- 30. What properties do most covalent compounds share? • When a covalent compound melts or boils, the covalent bonds holding the molecules together do not break as ionic bonds in an ionic compound do. • Instead, one molecule separates from another. • Because molecules separate easily from other molecules, they tend to have lower melting and boiling points than ionic compounds.
- 31. What properties do most covalent compounds share? • Most covalent compounds are poor conductors of electric current in both solid and liquid form. • Unlike ions, which are charged, molecules are neutral. • So, even in a liquid in which molecules can move around, the compound cannot conduct electric current.
- 32. Free to Move How does a metallic bond form? • A metallic bond forms between metal atoms when their outermost energy levels overlap. • Metallic bonding is weak compared to ionic or covalent bonding. • You can think of a metal as being made up of positive metal ions with enough valence electrons “swimming” around to hold the ions together. • https://www.youtube.com/watch?v=b1y2Q6YX1bQ
- 33. How does a metallic bond form? • Copper metal is held together by metallic bonding, in which electrons flow around copper ions.
- 34. What properties do most metallic compounds share? • Because the electrons in a metal can move freely, most metals are good conductors of electric current. • When you turn on a lamp, valence electrons move through the copper wire that connects the light bulb to the electrical outlet. • The valence electrons in the copper atoms are free to move because they are not connected to any one atom.
- 35. What properties do most metallic compounds share? • Due to their free-moving electrons, metals have two properties that allow them to be reshaped. • Malleability is the ability to be hammered into sheets. • Ductility is the ability to be formed into long, thin wires.