Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. first shella maximum of 2 electrons second shella maximum of 8 electrons third shella maximum of 8 electrons Bigger energy level = higher energy ATOMIC STRUCTURE
With the Bohr Diagram ( Dot & Cross diagrams) elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; Nitrogen XXX X XX X N 7 14 ATOMIC STRUCTURE: Bohr Diagram 7P+ 7n0
Bohr Diagrams Draw the Bohr Diagram for the following elements: OCl 817 16 35 a)b) 8p+ 8n0 X X X X X X X X 17p+ 18n0 X X X XX X XX X X X X X XX XX
Draw the Bohr Diagram for the following elements: Bohr Diagrams BNe 510 11 20 c)d) 5p+ 6n0 X X X X X 10p+ 10n0 X X X X XX X X X X
Valence Electrons The electrons on the outermost energy level These electrons determine the element’s chemical properties and its ability to form chemical bonds.
Lewis Structure of Atom The chemical symbol for the atom is surrounded by a number of dots corresponding to the number of valence electrons. Examples –Hydrogen atom has 1 valence electron H –Fluorine atom has 7 valence electrons F
Lewis Structure Draw the Lewis Structure for the following elements: a) Li b) Cl c) P d) Mg
Chemical Bonds Atoms react with one another to fill their outer energy levels Transferring or sharing electrons creates an attraction (chemical bond) that holds atoms together
2p2n 10p10n 18p22n He 4 2 10 20 Ne Ar 40 18 2,8 2,8,8 Noble Gases Helium, neon and argon are atoms which do not react with other atoms. We call them “Noble Gases” because of this. Each of these gases has a full outer electron shell.
IONIC BONDS Ionic bond: one atom transfers an electron to another atom Oppositely charged ions are attracted to one another forming a chemical bond an ionic bond
Na e.c. 2,8,1 (Na + ) Ion Atom e.c. (2,8) + The Sodium loses 1 electron to leave a complete outer shell. It is now a Sodium ion with a charge of 1 + The Sodium atom has 1 Electron in it’s outer shell. +
Cl e.c. 2,8,7 (Cl - ) Ion Atom e.c. (2,8,8) - The Chlorine gains 1 electron to gain a complete outer shell. It is now a Chlorine ion with a charge of 1 - The Chlorine atom has 7 electrons in it’s outer shell. -
Sodium atom Na Sodium ion (Na + ) Chlorine atom Cl Chlorine ion (Cl - ) The Ionic Bond The sodium atom loses one electron to attain a complete outer shell and become a positive ion (Na + ). The Chlorine atom gains one electron to attain a complete outer shell and become a negative ion (Cl – ). Strong forces attract the sodium and chlorine ions. +-
Covalent Bond Formed when atoms share electrons Electrons may be shared equally or unequally Molecule: two or more atoms held together by covalent bonds