Atoms and Molecules

Nestor T. Hilvano, M.D., M.P.H.(Images Copyright Discover Biology, 5th ed., Singh-Cundy and Cain,

Textbook, 2012.)

Learning Objectives

1. Definition of terms: matter, element, compound, atom, molecule, isotopes, ionic bond, covalent bond, and H bond.

2. Describe the structure of an atoms. 3. Discuss the beneficial and harmful effects of isotopes

in man.4. List 4 major elements of the human body. 5. Differentiate the types of chemical bonds. 6. What is H bond and give it’s importance?

• ___ What is everything around you that occupies space and has mass (composed of elements)?

• ___ What substances cannot be broken down into simpler (other) substances?

• 96% of the human body

is composed of 4

elements (COHN)• 7 major minerals/electrolytes:

Ca++, P, K+, Na+, Cl-, Mg++, S• 16 trace elements: Fe, I • Elements b. Molecules

c. Matter d. Compounds

Atoms • Smallest unit of matter • Subatomic particles a. Protons -positive charge (in the nucleus of an atom)

b. neutrons -no charge (in the nucleus)

c. electrons -negative charge (orbit in shells around the nucleus)

• Atomic number- tells us the no. of p+ and also the no. of e-

• Atomic mass (weight)- equals the no. of p+ and no. of nº

• Number of nº = atomic weight – atomic number• i.e. C (atomic no. 6, atomic mass 12)

O (atomic no. 8, atomic mass 16) H (atomic no. 1, atomic mass 1) Na (atomic no. 11, atomic mass 23) Cl (atomic no. 17, atomic mass 35)

http://www.design564.com/wp-content/uploads/2010/09/periodic_table_of_elements1.jpg

Figure 2.3A

Helium

2e

Nucleus

Electroncloud

2

2

2

Protons

Neutrons

Electrons

Mass number 4

2 He 4

Isotopes • Atoms of the same element but have different

numbers of neutron

- isotopes of Carbon (C-12, C-13, C-14)• Radioactive (unstable) isotopes- nucleus decays

giving off particles and energy (ex. C-14, N-16)• Harmful effects – cause disease, birth defects,

death • Uses or beneficial effects – markers or tracers,

diagnostic procedures, treatment

http://terra.dadeschools.net/Books/Biology/BiologyExploringLife04/0-13-115075-8/text/chapter4/04images/04-05.gif

Chemical Bonds• Electrons- part of an atom that interact; arranged in shells

- innermost shell = full w/ only 2e- outermost shell = up to 8e

• Atoms whose outermost shell are not full will participate in a chemical bonds

• Exercises: Give the no. of electron shells and no. of electrons in the outermost shell (valence electrons) of the ff.: Na (atomic no. 11), H (atomic no. 1), C (atomic no. 6), N (atomic no. 7), O (atomic no. 8), Cl (atomic no. 17); and

Mg (atomic no. 12)

Figure 2.5_1

Hydrogen

Lithium

Sodium

Beryllium

Magnesium

Boron

Aluminum

Carbon

Silicon

Nitrogen

Phosphorus

Oxygen

Sulfur

Fluorine

Chlorine

Helium

Neon

Argon

Chemical Bonds

• # of shells determined by # of protons (electrons)• atoms want the outermost shell to be filled

=STABILITY

Ionic Bonds • Attraction of ions of opposite charges,

Gaining or losing of electrons

• Ions are atoms with an electrical charge resulting from a gain of e-, anion; or loss of e-, cation.

• Ionic bond- ex. NaCl

• Weak bond- salt dissolves in water

Figure 2.7A_s2

Transfer of electron

NaSodium atom

ClChlorine atom

Na

Sodium ionCl

Chloride ion

Sodium chloride (NaCl)

Na (atomic no. 11, atomic mass 23)Cl (atomic no. 17, atomic mass 35)

Covalent bonds • Molecule – 2 or more atoms

held together (ex: O2) • Compound- 2 or more types of

atoms (different elements) joined together (ex: CO2)

• Covalent bonds – 2 atoms share one or more pairs of outer shell electrons; very strong bond

• a) Nonpolar covalent bond -electrons are shared equally between the atoms (H2, O2, CH4).

• b) polar covalent bond -unequal sharing of electrons (H2O).

Weak Chemical Bonds • Hydrogen (H) bonds- weak bonds as in H20 molecules

• Importance: occur in other biological compounds like proteins and DNA, form bridges between molecules

http://www.elmhurst.edu/~chm/vchembook/162othermolecules.html

http://www.dna-sequencing-service.com/dna-sequencing/dna-hydrogen-bonds-2/

Homework (Self Review)

1. Define terms: matter, atom, element, molecule, compound, ionic bond, covalent bond, polar covalent bond, nonpolar covalent bond, ion, anion, cation, and isotopes.

2. Name and describe the 3 subatomic particles of an atom.

3. List the 4 major elements of the human body.4. Discuss how isotopes cause harmful effects to

human. 5. Oxygen has atomic number of 8. What is the

number of valence (outermost) electrons?