Atoms and Subatomic Particles Ch 4. Section 2

How big is an atom? An atom is incredibly small The diameter of an atom would have to be increased 200 million times to have the diameter of a penny If an apple were enlarged to the size of the Earth, the atoms in the apple would be the size of cherries

What is an atom made of? Subatomic particles: Neutron, proton, electrons A central, dense nucleus (neutrons & protons) surrounded by electrons Electrons have a negative charge (-) Protons have a positive charge (+) Atom is held together by the attraction of electrons and protons Neutrons are neutral

How much does an atom weigh? (What is it’s mass?) Atoms are so small that it is impractical to use grams 1 atom ͌ 10-23 g Instead atoms are measured in atomic mass units or amu’s One carbon atom is 12.0 amu’s and all atoms are compared to this

Atoms - Molecules - Ions Subatomic Particles Particle Mass (kg) Mass (amu) Charge Electron 9.10939 x 10-31 0.00055 -1 Proton 1.67262 x 10-27 1.00728 +1 Neutron 1.67262 x 10-27 1.00728 0 Most of the mass in an atom is in the nucleus

ATOMIC FACTS Most of the mass of an atom is in the nucleus: the protons and neutrons The size of the neutron relative to the size of the atoms is like a penny in the middle of a baseball field The number of protons and electrons need to be equal so that the atom has no charge

ATOMIC NUMBER The number of protons in the nucleus of an atom Atomic numbers of naturally occurring elements: Lowest=Hydrogen (H) Z=1 Highest=Uranium (U) Z=92 Periodic Table of Elements

ATOMIC NUMBER Remember, The number of protons in the nucleus of an atom equal the number electrons so, Atomic number= Number of protons= Number of electrons

Mass Number Sum of the number of protons and the number of neutrons in the nucleus of the atom: Mass number=# of protons + # of neutrons And….. Mass number=atomic number + # of neutrons # of neutrons=mass number – atomic number

Isotopes Atoms of an element that have the same number of protons and electrons but different numbers of neutrons. Hydrogen isotopes Hydrogen has 1 proton, 1 electron and 0 neutrons Deuterium has 1 proton, 1 electron and 1 neutron Therefore, it is heavier than hydrogen but has similar chemical properties and slightly different physical properties Tritium has 1 proton, 1 electron and 2 neutrons

Atomic Masses Atomic mass ͌ Mass number Here’s why They are close but not the same Here’s why Mass number is an exact number & atomic mass is a weight so it’s an inexact number Hydrogen has a mass number of 1 (1 protron + 0 neutrons), But weighs: 1.00728 amu Atomic masses are calculated based on the percentage of isotopes present in natural world H=99.985%; D=.015%; T=trace Atomic mass of H is: 1.00794 Periodic table of elements

Chemical Basis of Life Most common elements in living organisms Carbon (C): 9.5% Hydrogen (H): 63% Oxygen (O): 25.5% Nitrogen (N): 1.4%

Macrominerals Minerals we need a lot of Calcium (Ca) Phosphorous (P) Magnesium (Mg) Potassium (K) Sodium (Na)

Microminerals Needed in small quantities Iron (Fe) Copper (Cu) Chromium (Cr) Fluoride (F) Iodine (I) Selenium (Se) Molybdenum (Mo) Zinc (Zn)