Elements and Life

Basic chem. review

Elements and Compounds• Organisms are made of Matter. Which is composed of

elements.• An element is a substance that cannot be broken

down any further. (atoms)• A compound is a substance consisting of two or more

elements in a fixed ratio (molecules).

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Table 2-1

Fig. 2-4a

(a) Nitrogen deficiency

Fig. 2-4b

(b) Iodine deficiency

Secondshell

Thirdshell

Hydrogen

1H

Lithium

3LiBeryllium

4BeBoron

5BCarbon

6CNitrogen

7NOxygen

8OFluorine

9FNeon

10Ne

Helium

2HeAtomic number

Element symbol

Electron-distributiondiagram

Atomic mass

2He

4.00Firstshell

Sodium

11NaMagnesium

12MgAluminum

13AlSilicon

14SiPhosphorus

15PSulfur

16SChlorine

17ClArgon

18Ar

Electrons • Electrons are found around the outside of the

nucleus of atoms

• Valence electrons are those in the outermost shell or energy level

• Atoms seek to have a full outer energy level.

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Valence electrons

Bonding• * Atoms bond so that their outer energy level will be full

(contain 8 electrons, 2 for hydrogen) *

Covalent Bonding• atoms combine by sharing electrons in their outer

energy level (Water)• - shared electrons move around both atoms.• - covalent bonds produce molecules.• Ex. Water Molecule (H20)

Polar Covalent Bonds• - a polar covalent bond occurs when electrons are

shared unequally. The stronger atom’s nucleus pulls the electrons closer than the weaker atom’s. The strong atom becomes slightly negative, the weaker atom becomes slightly positive. (ex. water)

• Ex. Water(H20) polar

+

+

-

Fig. 2-13

–

+ +H H

O

H2O

Non-Polar Covalent Bonds• - a non-polar covalent bond occurs when electrons

are shared equally. (example oxygen gas)• Ex. Chlorine gas(Cl2)

Ionic Bonding• Ionic Bonding – a atoms combine by gaining or loosing

electrons. (to get a full outer energy level)• - the metal gives electrons to the non-metal and becomes

positive (cation- a positive ion)• -the non-metal accepts electrons from the metal and

becomes negative (anion- a negative ion) • - since they are oppositely charged, they stick together

(bond) ex NaCl

Goes to Cl

Cl slightlynegative

Na slightlypositive

Fig. 2-14-2

Na Cl Na Cl

NaSodium atom Chlorine atom

Cl Na+

Sodium ion(a cation)

Cl–

Chloride ion(an anion)

Sodium chloride (NaCl)