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

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

Elements with more valence electrons are less reactive

Electron Dots and the Periodic Table

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

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

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

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

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

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

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

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

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

Ions and Their Charges

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

Sodium Chloride

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

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

Chemical formula

-ide ending

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

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

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

Sharing Electrons

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 Covalent bonds

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

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

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

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

Fluorine and Hydrogen

Water = Polar Molecules

Carbon dioxide = non-polar

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

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

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

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

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

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

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

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