Physical Science: Ch 6 Notes A. Atoms Bond to form Compounds Compound- a substance that is composed of two or more different elements joined in a fixed proportion Chemical bond- the force that holds atoms together Covalent bond- a chemical bond in which two atoms (both nonmetals!) share a pair of valence electrons Ionic bond- a chemical bond that forms between atoms of a metal and a nonmetal Form when electrons are transferred from one atom to another Results in the formation of ions – atoms that have a net positive or negative electric charge This charge is due to the loss or gain of electrons This transferring of electrons allows electricity to flow through solutions of ionic compounds

Physical Science: Ch 6 Notes Cation – an ion with a positive charge (due to loss of electrons) Anion – an ion with a negative charge (due to gain of electrons) Naming ionic compounds examples: magnesium chloride copper sulfide zinc oxide the trend: cation anion-ide Molecule – a neutral group of atoms (nonmetals!) that are joined together by one or more covalent bonds The attractions between the shared electrons and the protons in each nucleus hold the atoms together in a covalent bond Molecules are named using prefixes that describe the number of atoms of each element in the molecule

Physical Science: Ch 6 Notes Prefixes for naming COVALENTLY bonded molecules: 1=mono6=hexa 2=di7=hepta 3=tri8=octa 4=tetra9=nona 5=penta10=deca Examples: N 2 O 4 is dinitrogen tetraoxide P 3 F 7 is triphosphorus heptafluoride NO 2 is nitrogen dioxide NOTICE: the second element still ends in –ide the prefix mono is not usually used for the first element in the name (NO 2 is nitrogen dioxide) REMEMBER: When naming chemicals, prefixes are only used when nonmetals are bonded (COVALENT MOLECULES)! Prefixes are NOT used for naming Ionic Compounds.

Physical Science: Ch 6 Notes B. Properties of Ionic and Covalent chemicals IONICCOVALENT -usually solid at room temperature -have high melting and boiling points -forms solid crystals -solutions of ionic compounds conduct electricity -usually dissolve in water very well -usually liquid or gas at room temp -lower melting and boiling points -does not form solid crystals -solutions do not conduct electricity -usually do not dissolve in water very well

Physical Science: Ch 6 Notes C. Metals Alloy – a mixture of two or more elements, at least one of which is a metal Bronze – alloy of copper and tin metals Brass – alloy of copper and zinc metals Steel – alloy of iron with small quantities of carbon