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Chapter 5 Atoms, Bonding and the Periodic Table 8 th Grade Science.

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Presentation on theme: "Chapter 5 Atoms, Bonding and the Periodic Table 8 th Grade Science."— Presentation transcript:

1 Chapter 5 Atoms, Bonding and the Periodic Table 8 th Grade Science

2 Valence Electrons and Bonding ____________ - electrons that have the highest energy level and are held most loosely. The number of valence electrons that an element has determines the ways in which the atom can _____with other atoms. Each element has a specific number of ____________ ranging from 1 to 8. ______________ - includes the symbol for the element surrounded by dots that represent the valence electrons. Valence electrons Bond Valence electrons Electron-dot diagram

3 Elements with more valence electrons are less reactive

4 Electron Dots and the Periodic Table

5 Chemical Bonds and Stability ____________ - force of attraction that holds two atoms together. When atoms bond, ________ may be transferred from one atom to another, or they may be shared between the atoms. The result of chemical bonding is a ____________ where a new substance is formed. Chemical Bond electrons Chemical reaction

6 Relating Periods and Groups As the _____________ of an atom increases, the number of electrons increases as you move from the left side of the periodic table to the other. Remember: a ________ on the periodic table is a row from left to right. A _________ ends when the number of valence electrons equals __. The next period will have a higher _________ than the one before. Atomic Number period 8 Energy level

7 Patterns of Valence Electrons Elements within a ______ or a column always have the same number of ____________. Group 1 elements have ___ valence electron Group 2 elements have ___ valence electrons Each group has one more valence electron than the one to its ____. The elements within a group have similar properties because they all have the same number of ____________ in their atoms. group Valence electrons 1 2 left Valence electrons

8 Noble Gases Group _____ Atoms have ____ valence electrons, except for Helium These atoms are ______ - less reactive – unlikely to transfer or share electrons with other atoms. 18 8 stable

9 Reactive Metals and Non-metals Halogens in Group ___ have ____ valence electrons. Halogens are therefore more reactive than the __________. Alkali Metals in Group ___ - have ___ valence electron. Alkali metals are ___________. How reactive a metal is depends on how easily its atoms lose valence electrons. 177 Noble Gases 1 1 Very reactive

10 Other Metals and Non-Metals The reactivity of metals decreases from left to right across the periodic table. In Groups one and 2, reactivity increases from _____ to _______. Non-metals – most are _____ at room temperature, five are ______, and one is ______ Non-metals combine with metals by ______ an electron topbottom gases solids liquid gaining

11 Metalloids Non-metals combine with other ___________ by ________ electrons _________ lie along the zig-zag line between metals and non-metals. Metalloids have between ______ valence electrons. Metalloids can either _____ or ________ electrons depending on the conditions – behave as both metals and non-metals Non-metals sharing metalloids 3 to 6 loseshare

12 Hydrogen ____ valence electron Considered to be a ___________ ___________ but its properties differ greatly from those of the alkali metals 1 Non-metal reactive

13 Ions _____ - an atom or a group of atoms with an electric charge. When an atom _______ an electron it loses a _______ charge and becomes a ________ ion. When an atom _____ an electron, it _____ a negative charge and becomes a _______ ion. ____________ - ions that are made of several atoms – have an overall positive or negative charge. ion negativepositive loses gains negative Polyatomic ions

14 Ions and Their Charges

15 Ionic Bonds __________ - the attraction between two oppositely charged ions. Ionic bonds form as the result of the attraction between positive and negative ions A compound that consists of both positive and negative ions (sodium chloride) is an ______________. Ionic bonds Ionic compound

16 Sodium Chloride

17 Chemical Formulas and Names _____________ - a combination of symbols that shows the ratio of elements in a compound. _____________ - charges of the ions are balanced – the chemical formula represents the balance _________ - represents the ratio of elements in the compound. * if there is no subscript – 1 is understood. Chemical Formula Ionic compounds subscript

18 Naming Ionic Compounds The name of the _________ ion comes before the _______ ion. Example: magnesium chloride, sodium bicarbonate, sodium oxide _______ - negative ion is a single element ____________ - negative ion is polyatomic – ammonium nitrate positive negative -ide ending -ate or ite ending

19 Chemical formula

20 -ide ending

21 Properties of Ionic Compounds _____________ - hard, brittle crystals with high melting points When ionic compounds are dissolved in water, they ____________. _______ - ions form an orderly three dimensional arrangement. ______________ - heat increases energy levels – when ions have enough energy to overcome the attractive forces between them, they break away from each other and melt. Ionic compounds Conduct electricity crystal High melting points

22 Electrical Conductivity ___________ - flow of charged particles Ions that are dissolved in water as a result of___________, are able to move _______ and the solution is able to conduct electricity. Electric current Broken bondsfreely

23 Covalent Bonding _____________ - chemical bond that is formed when two atoms SHARE electrons. Covalent bonds usually form between ___________. Ionic Bonds usually form between a _____ and ________ __________ - neutral group of atoms joined by covalent bonds Covalent Bond nonmetals metal nonmetal molecule

24 Sharing Electrons

25 Covalent Bonds and Valence Electrons The number of _____________that nonmetals can form equals the number of electrons needed to make a total of ____. ___________ - is the exception – only needs __. Water Molecule – oxygen has __ valence electrons. Hydrogen has __ valence electron. Therefore, oxygen forms two __________ with hydrogen. eight Covalent bonds Hydrogen 2 6 1 Covalent bonds

26 Double Bonds and Triple Bonds A set of eight valence electrons makes the covalent bonded molecule _______ __________ is the exception – hydrogen only needs ___ electrons to be stable ___________ - a chemical bond formed when atoms share two pars of electrons - carbon ___________ - a chemical bond formed when atoms share three pairs of electrons - Nitrogen stable Hydrogen 2 Double bonds Triple Bonds

27 Molecular Compounds _______________ - a compound that is composed of molecules of atoms that are covalently bonded. Molecular compounds have ________________ and ____________ than ionic compounds. Molecular compounds DO NOT _____________. Molecular compound Lower melting pointsBoiling points Conduct electricity

28 Melting points/ Boiling Points/ Conductivity Molecular compounds have ________ attractive forces between molecules. Ionic compounds have _____ attractive forces between the molecules Therefore, ___energy is needed to melt molecular compounds. Molecular compounds do not conduct electricity because there are _____________ weak strong less No charged particles

29 Polar Bonds / Non-Polar Bonds _________ - a covalent bond in which electrons are shared unequally – The atom with the stronger pull will become slightly ________, the weaker atom will become slightly _______. _____________ - a covalent bond in which the electrons are shared equally. Polar Bonds negative positive Non-polar Bonds

30 Fluorine and Hydrogen

31 Water = Polar Molecules

32 Carbon dioxide = non-polar

33 Alloys ____ - a mixture made of two or more elements that has the properties of metal In every alloy at least one of the elements is a ________. Alloys are ______ and less likely to react with air or water unlike the pure metals from which they are made. alloy metal stronger

34 Physical / Chemical Properties Physical properties can be different from those of the individual _________ that alloys are made of. Depending on how they are mixed, alloys retain many of the __________ properties of metals. Elements like iron are often mixed with other elements such as carbon, nickel, and chromium to prevent _____ - a chemical reaction that occurs when iron is exposed to air or water – examples = steel used in forks. elements physical rusting

35 Metallic Bonding Metals _______ electrons easily because their __________ electrons are not strongly held. Metal atoms are held very closely and in a specific arrangement – metals exist as _______ Each metal ion is held in the ______ by a ___________. ___________ - an attraction between a positive metal ion and the valence electrons surrounding it. lose valence crystals crystal Metallic bond

36 Metallic Bonds Continued Solid metals consist of positively charged ions surrounded by loose _______________. The _____ valence electrons an atom can add the _______ the metallic bond. Question: Which are stronger metallic bonds or ionic bonds? Valence electrons metal stronger

37 Metallic Properties _____________ explains many of the common physical properties of metals and their alloys. _____________ - metals can be stretched, compressed, or pushed into different shapes because the __________ are attracted to the loose electrons all around them rather than to other metal ions. – Metallic bonds between the ion and the surrounding electrons keep the metal from breaking. Metallic Bonding Changes in shape Positive ions

38 Other Metallic Properties _________________ - metals conduct electricity easily because their electrons can move freely among the atoms. – When connected to a battery, the _________ will run into the metal at a certain point and out of the metal at another point. ________ - polished metals are shiny and reflective. When light hits a metal’s _____________ they absorb the light and give it off again. Electrical conductivity current luster Valence electrons

39 Heat Conductivity Heat causes particles of matter to move ______ If these particles collide with cooler particles of matter, thermal ______ is transferred to the cooler particles. _____________ valence electrons transfer energy from nearby atoms and other electrons – heat travels easily through a metal or a metal alloy. faster energy Freely moving

40 Growing Copper Sulfate Crystals Materials: One egg, plastic container, measuring apparatus, spoon for stirring, and copper sulfate Procedures: 1 Crack an egg carefully to get two fairly even halves. Discard the inside of the egg and gently wash the shell in warm water. 2 Place the eggshells in a plastic container on a paper towel. LABEL 3 Pour 0.25 cups of hot water into a clean glass jar. Add 1 to 1.5 tsp. of copper sulfate to the water and stir with a spoon. 4 Carefully pour the copper sulfate solution into the halves of the eggshells. Place the container with the eggshells in the chemical hood. 5 Let the solution sit in the eggshells for several days until the desired amount of crystals have formed. 6 Look at crystals under the microscope

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