ATOMS, IONS, MOLECULES
ATOM: SMALLEST BASIC UNIT OF
MACROSCOPIC : a penny
MICROSCOPIC : atoms
ELEMENT: SUBSTANCE WITH ONLY THE
SAME TYPE OF ATOMS
Only gold atoms Only hydrogen
ELEMENTS IN ORGANISMS
96% of human body’s mass is made of CARBON
(C), OXYGEN (O), NITROGEN, HYDROGEN (H)
4% of human body’s mass is CALCIUM (Ca),
PHOSPHORUS (P), POTASSIUM (K), SULFUR
(S), SODIUM (Na)
COMPOUND: SUBSTANCE W/ TWO OR
MORE DIFFERENT TYPES OF ELEMENTS
COMPOUNDS IN LIVING THINGS
Carbon dioxide (CO2)
IONS: ATOM THAT GAINED/LOST
Positive ion: lost electrons
Negative ion: gained electrons
Ionic bond: ions held together by attraction of +
and – charges
IONS IN YOUR BODY
Hydrogen ions (H+): needed in cells to produce
usable chemical energy
Calcium ions (Ca2+): muscle movement
Chlorine ions (Cl-): chemical signals in brain
COVALENT BOND: WHEN ATOMS
SHARE A PAIR OF ELECTRONS
Molecule: two or more atoms held together by
Almost all substances that make up organisms
are molecules held together by covalent bonds
WATER AND ITS FUNCTION
WATER IS A POLAR MOLECULE.
Polar molecules have slightly charged regions.
– Nonpolar molecules do not have charged regions.
– Hydrogen bonds form between slightly
positive hydrogen atoms and slightly negative
Hydrogen bonds are responsible for three important
properties of water.
1. high specific heat: water can resist changes in
• Water absorbs heat during cell processes to
help regulate cell temperature.
2. Cohesion: molecules attract each other in a
• Produces surface tension.
3. Adhesion: molecules of different substances
attract each other.
• Water in glass tube.
MANY COMPOUNDS DISSOLVE IN WATER.
A solution is formed when one substance dissolves in
A solution is a homogeneous mixture.
Solvents dissolve other substances.
Solutes dissolve in a solvent.
“Like dissolves like.”
– Polar solvents dissolve polar solutes.
– Nonpolar solvents dissolve nonpolar solutes.
– Polar substances and nonpolar substances
generally remain separate.
SOME COMPOUNDS FORM ACIDS OR BASES.
An acid releases a hydrogen ion when it dissolves in
high H+ concentration
pH less than 7
stomach acid pH between 1 and 3
A base removes hydrogen ions from a solution.
– low H+ concentration
– pH greater than 7
bile pH between 8 and 9
A neutral solution has a pH of 7.
pure water pH 7
PH IN ORGANISMS
Humans need to stay near neutral pH
Small changes in pH can disrupt cell processes
Azalea plans thrive in high pH soil