Elements: Building Blocks of Minerals

Earth Science

Chapter 2 Section 1

BELLWORK:

●About 14 elements make up the earth’s crust. Silicon (Si) comprises about 28% of the earth’s crust. Another important element constitutes almost 47% of the crust. Read the three clues to help you find out which element it is.

●Clue #1: Two of its letters often appear as unknowns in algebra.●Clue #2: It can be generated from mercuric oxide.●Clue #3: At room temperature, it is as light as air.

●What is the element?

TODAY’S OBJECTIVES:

●Describe the basic structure of an atom and explain how atoms combine.●Explain isotopes and radioactive decay.

ELEMENTS

●Cannot be broken into simpler substances.●Made of atoms (from Greek: a = not, tomos = cut).

●Protons – positive charge; found in the nucleus●Neutrons – neutral charge; found in the nucleus●Electrons – negative charge; found in the electron cloud

●About 90 naturally occurring.●Arranged according to properties in Periodic Table

ATOMIC NUMBER

●The number of protons in the nucleus of an atom.●Equal to the number of electrons in the electron cloud.

Mass Number

●The average mass of the element●When rounded to the nearest whole number, equals the #protons + #neutrons

Try it out…

●This is the element helium.

●What is the atomic number?●What is the mass number?●How many protons does helium have?●How many electrons?●How many neutrons?

Electrons

● Move around the nucleus in principal shells, almost like layers.

● The outermost layer contains the valence electrons, which are used to bond elements together.

ATOMIC BONDS●Atoms are stable when they have 8 valence electrons.●Atoms will give up, take on or share electrons to reach their “magic number.” ●Ionic Bonding

●One atom gives up electrons while another atom takes them on.●Compounds are rigid, and brittle●Common ionic compounds: table salt, sugar,

●Covalent Bonding●Atoms share electrons so that both have 8 valence electrons.●Compounds are “squishy” compared to ionic compounds●Common covalent compounds: water, ammonia, and methane

Isotopes and Radioactive Decay

●Isotopes are atoms with extra neutrons

●They are heavier than the traditional atom of that element●Common Isotopes:

●Hydrogen (Deuterium and Tritium) ●Carbon

●Some isotopes have unstable nuclei●Atoms will break down over time into other substances●Can be used to measure time or identify the age of an object