5.1 How Atoms Form Compounds. compound chemical formula molecule chemical bond ionic bond valence covalent bond

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1 5.1 How Atoms Form Compounds compound chemical formula molecule chemical bond ionic bond valence covalent bond

2 What is a compound? 5.1 How Atoms Form Compounds A compound is a pure substance that contains two or more elements. Compounds are chemical combinations of elements with properties that are different from the elements that formed them.

3 5.1 How Atoms Form Compounds Chemical Formulas for Compounds A chemical formula contains atomic symbols and subscripts to show the elements and the number of atoms of each element in the compound.

4 Describing Compounds 5.1 How Atoms Form Compounds A water molecule, or H 2 O, is two hydrogen atoms bonded to one oxygen atom. The subscript number shows how many atoms the element are in the compound. A molecule is a neutral particle that forms as a result of electron sharing. How can a molecule model be built?

5 Describing Compounds (cont.) 5.1 How Atoms Form Compounds The chemical formula for sucrose, C 12 H 22 O 11, includes all the atoms in one molecule.

6 5.1 How Atoms Form Compounds Compounds and Their Elements Compounds have different properties than the elements that make them up. Sodium chloride is table salt. Sodium is a soft metal. Chlorine is a greenish-yellow gas.

7 5.1 How Atoms Form Compounds Ionic Bonds and Ionic Compounds A chemical bond is a force that holds atoms together in a compound. An ionic bond is an electrical attraction between positively and negatively charged ions in an ionic compound.

8 5.1 How Atoms Form Compounds Ionic Bonds Transferring Electrons An atom can become charged by transferring one or more electrons to another atom. Both atoms become charged particles, or ions.

9 5.1 How Atoms Form Compounds Ionic Bonds Transferring Electrons A lithium atom gives up an electron to a fluorine atom. The result is a positively charged lithium ion and a negatively charged fluoride ion. (cont.)

10 5.1 How Atoms Form Compounds Ionic Bonds Transferring Electrons The two ions have opposite charges and are attracted to each other. Lithium fluoride is the simplest type of compound, made only of two elements and known as a binary compound. (cont.)

11 Ionic Compounds 5.1 How Atoms Form Compounds Elements in the same column on the periodic table form a group. Metals in Group 1 can transfer 1 electron and will become +1 ions. Non-metals in Group 17 can gain an electron to form 1 ions. When a positive ion from Group 1 and a negative ion from Group 17 combine, a salt like sodium chloride forms.

12 5.1 How Atoms Form Compounds Other Binary Ionic Compounds Group 2 elements are also metals and can lose 2 electrons and form ions with a +2 charge. Elements in Group 16 can gain 2 electrons and form ions with a 2 charge.

13 5.1 How Atoms Form Compounds Other Binary Ionic Compounds (cont.) Magnesium can transfer one electron to each of 2 Fluorine atoms to form magnesium fluoride (MgF 2 ).

14 5.1 How Atoms Form Compounds Properties of Ionic Compounds Usually solids at room temperature Brittle and break apart easily Have high melting and boiling points Many dissolve in water

15 Diagramming Electrons Lewis Dot Diagrams 5.1 How Atoms Form Compounds A Lewis dot diagram is a system to represent atoms and their electrons. You must know the number of valence electrons an atom has. Valence electrons are the electrons in the outermost energy level. Valence and Lewis Dot Diagrams

16 Noble Gas Structure by Gaining Electrons Chlorine can achieve noble gas structure by filling its outer energy levels. Argon is the nearest noble gas to chlorine. Chlorine can become more stable by gaining one electron and forming the chloride ion Cl. 5.1 How Atoms Form Compounds

17 Noble Gas Structure by Losing Electrons 5.1 How Atoms Form Compounds Magnesium can achieve the electron structure of neon, the nearest noble gas on the periodic table. Magnesium can lose two electrons to form the stable ion Mg 2+.

18 5.1 How Atoms Form Compounds Covalent Bonds Sharing Electrons Ionic bonds form when electrons are transferred. Some elements need to gain or lose too many electrons. A covalent bond is a chemical bond formed when atoms share electrons.

19 Covalent Bonds Sharing Electrons Carbon has 4 valence electrons. 5.1 How Atoms Form Compounds Too much energy is needed for carbon to easily gain or lose 4 electrons. (cont.)

20 5.1 How Atoms Form Compounds Covalent Bonds Sharing Electrons (cont.) Elements that are close together on the periodic table are more likely to share electrons in a covalent bond than to transfer electrons. Organic compounds are covalent compounds containing carbon atoms and are important for living organisms.

21 Properties of Covalent Compounds Can be solids, liquids, or gases at room temperature Usually have lower melting and boiling points than ionic compounds Do not usually separate in water Most do not conduct electricity 5.1 How Atoms Form Compounds

22 Single Covalent Bonds 5.1 How Atoms Form Compounds Hydrogen has one unpaired electron. Two hydrogen atoms share their single electrons to form a pair. The shared pair of electrons is a single covalent bond, which holds the hydrogen molecule H 2 together.

23 Double and Triple Bonds 5.1 How Atoms Form Compounds Some atoms may form stronger bonds by sharing more than one pair of electrons. A double bond has two pairs of shared electrons and is stronger than a single bond. A triple bond has three pairs of shared electrons and is stronger than a double bond.

24 5.2 Forming Solids metal metallic bond malleability ductility crystal unit cell polymer monomer

25 Metals 5.2 Forming Solids Metals are elements that are usually shiny, good conductors of electricity and heat, and solid at room temperature.

26 Metallic Bonds A metallic bond is formed when many metal atoms share their pooled electrons. Metal atoms can bond to atoms of the same element, or to other metals. 5.2 Forming Solids

27 Bonding and Properties Metals are good conductors because their electrons move freely. Metals can be hammered into sheets or pulled into wires without breaking. 5.2 Forming Solids

28 Metal Atoms and Patterns 5.2 Forming Solids Metal atoms combine in a regular pattern in which some electrons are free to move about.

29 Physical Properties of Metals 5.2 Forming Solids Malleability is the ability of a metal to be hammered or rolled into sheets. Ductility is the ability of a substance to be pulled into a wire.

30 Crystals 5.2 Forming Solids A crystal is a regular, repeating arrangement of atoms, ions, or molecules. Crystals are formed from repeating patterns. A unit cell is the smallest repeating pattern that shows how atoms, ions, or molecules are arranged in a crystal.

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32 What is a polymer? 5.2 Forming Solids A polymer is a covalent compound made up of many repeating units linked together in a chain. A monomer is a single molecule that forms a link in a polymer chain. Many hundreds of monomers link together to form a solid polymer.

33 Synthetic Polymers 5.2 Forming Solids Synthetic polymers, such as polyethylene, are polymers manufactured by humans.

34 Natural Polymers 5.2 Forming Solids All living cells must contain three important kinds of natural organic polymers proteins, carbohydrates, and nucleic acids.

35 Natural Polymers (cont.) 5.2 Forming Solids Amino acid monomers join together to form a protein. Protein and carbohydrate polymers shown with their monomers.