ELEMENTS Elements are substances that cannot be broken down chemically into simpler kinds of matter. >90% of all kinds of living things are made of combinations of 4 elements: OXYGEN (O 2 ) CARBON (C) HYDROGEN (H 2 ) NITROGEN (N)
CONNECTION Trace elements are common additives to food and water Trace elements are essential in minute quantities for proper biological functioning – Example: iodine is a trace element that prevents goiter – A goiter is an abnormal growth in the thyroid. – Many foods are fortified with trace elements and vitamins (which consist of two or more elements)
COMPOUNDS pure substance that is made up of atoms of two or more elements in a fixed ratio Different arrangements of the atoms of elements determine the unique properties of each compound Sodium (Na) is a soft metal that explodes when placed in water. Chlorine (Cl) is a green poisonous gas. Sodium Chloride (NaCl) is table salt.
ATOMS the simplest particle of an element that retains all of the properties of that element
Atoms consist of protons, neutrons, and electrons Subatomic particles – Protons and neutrons occupy the central region (nucleus) of an atom A proton has a single positive charge A neutron is electrically neutral – Electrons surround the nucleus An electron has a single negative charge
LE 2-4a 2 2 2 Protons Neutrons Electrons Helium atom Mass number = 4 6 6 6 Protons Neutrons Electrons Carbon atom Mass number = 12 Electron cloud Nucleus 2e – 6e –
Differences in Elements All the atoms of a particular element have the same number of protons The number of protons-the atomic number-defines the element's unique properties An atom's mass number (atomic mass) is the sum of its protons and neutrons
Isotopes Isotopes are atoms with the same atomic number but different atomic masses (different number of neutrons)
Common Isotopes and their uses Smoke Detectors and Americium-241 Smoke detection Food Irradiation
Radioactive isotopes can help or harm us Radioactive isotopes are useful as tracers to study the fate of elements and molecules in living systems Radioactive tracer isotopes are often used in combination with sophisticated imaging instruments for medical diagnosis Uncontrolled exposure to radioactive material can harm living organisms
Chemical Bonding The chemical reactivity of an atom depends on the number of electrons in the outer shell
Ionic Bonding Ionic Bonds: formed when one atom gives up an electron to another. The positive ion is then attracted to a negative ion to form the ionic bond. Form compounds An ion is a charged atom that has lost or gained electrons in its outer shell
Covalent Bonding Covalent Bonds: form when two atoms share one or more pairs of electrons A molecule consists of two or more atoms held together by covalent bonds.
Polarity In covalent bonds where the “sharing” is unequal Because of this uneven pattern of charge, water is a polar compound.