Mr. Conkey Physical Science Ch. 6 Chemical Bonds Mr. Conkey Physical Science Ch. 6

Stable Electron Configurations When the highest energy level of an atom is filled with e−’s, it is stable and unlikely to react Group 8 all have stable e− configurations (including He) Chemical properties depend on the # of valence e−’s Electron dot diagram – a model of an atom in which each dot represents a valence e−

Electron Dot Diagrams for some Group Elements

Ionic Bonds (e− Donors and e− Acceptors) Elements with incomplete sets of valence e−’s tend to react Some elements achieve a stable electron configuration through the transfer of electrons between atoms Example of electron transfer: Full Octet (now stable) e− donor e− acceptor Donated e− (also now stable Chlorine needs to gain one electron to be stable (See nearest Noble Gas, Argon); Sodium needs to lose one electron to be stable (to be like nearest Noble Gas, Neon)

Formation of Ions Ions – form when an atom gains or loses an electron and the number of protons and electrons become ≠ The charge on an ion is shown by a plus or minus sign (i.e. Na+ and Cl ‾ ) Cation – an ion with a positive charge (+) Anion – an ion with a negative charge ( ‾ )

Ionization Energy Cations form when e−’s gain enough energy to leave the atoms! The energy allows for the e−’s to overcome the attractive forces of the protons in the nucleus Ionization energy – the amount of energy needed to eject an e−

Ionic Compounds Ionic compounds – compounds that contain ionic bonds Chemical formula – a notation that shows the ratio of the atoms/ions of elements in a compound as well as what elements are in the compound Example: MgCl₂ Charges appear after electron transfer. Since Mg has a +2 charge, it needs to ionically bond to two Chlorine atoms (-1 charge)

Properties of Ionic Compounds Ionic compounds have high melting points, good conductors of electric current (when melted), and are brittle Ionic compounds tend to shatter when struck because the ions move from their fixed positions and like charges repel each other causing them to shatter

Covalent Bonds (sharing of e−’s) Nonmetals bond together using covalent bonds (two atoms sharing a pair of valence e−’s) and form a molecule Two Hydrogen atoms share their valence e−’s to form a stable e− configuration Molecule – a neutral group of atoms joined together by one or more covalent bonds H₂ Molecule

Molecules and Multiple Covalent Bonds Attractions between the shared e−’s and the protons in the nucleus hold atoms together in covalent bonds The amount of covalent bonds needed in a molecule depends on the # of valence e−’s of the atoms

Some Common Cations and Anions

Metallic Bonds Metallic bond – the attraction between a metal cation and the shared e−’s surrounding it Metallic bonds are relatively strong Electric current and malleability are due to the ability for the e−’s to move Pool of e−’s allow for good electric conductivity Cation and e−’s shifting allow for malleability

Alloys Alloy – a mixture of two or more elements (at least one has to be a metal!) Cu alloys: Bronze (Cu and Sn); two soft metals when mixed are much harder/stronger Brass (Cu and Zn); softer than bronze and easier to shape and shinier Brass Bronze

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Now the Battle of the Finals Begins!