The Atoms Family Chapter 1

What is an Element? A substance that cannot be broken down into simpler substances by physical or chemical means 92 occur naturally on the Earth and in stars Each is identified by a one-, two-, or three-letter abbreviation Some elements known in ancient times like gold and mercury, have symbols that reflect their Latin origins (gold-Au, Latin for Aurum)

The Smallest of All The smallest particle of an element that has all of the characteristics of that element is an atom Atoms are made of 3 things: protons, electrons, and neutrons Protons (positive) and neutrons (neutral) are in the nucleus Electrons (negative) are in energy levels surrounding the nucleus

Atoms Continued… The number of protons in the nucleus corresponds to the element’s atomic number The combined number of protons and neutrons in the nucleus is its atomic mass The number of protons and electrons is the same, resulting in an atom with no overall charge (charges cancel each other out)

Electron Energy Levels The number and arrangement of electrons determines the size of the atom Electrons move around the nucleus in energy levels and each can only hold so many electrons 1.1 st : 2 electrons 2.2 nd : 8 electrons 3.3 rd : 18 electrons 4.4 th : 32 electrons The number of electrons in the outermost energy level, called valence electrons, determines the chemical behavior of the element

Radioactivity When the number of neutrons in nuclei vary, you have an isotope For example, chlorine always has 17 protons, but the number of neutrons could be either 18 or 20. This in turn, changes the atomic mass The nuclei of some isotopes are unstable and release radiation During the radioactive decay process, the nuclei of these isotopes loses protons and neutrons The decay process changes the identity of an element, as in the case of Uranium-238 decaying into Lead-206

So, What Does This Mean to Earth Science? The 2 most abundant elements in the UNIVERSE are hydrogen (H) and helium (He) The 2 most abundant elements in the EARTH’S CRUST are silicon (Si) and oxygen (O) 98.5% of the Earth’s crust is made up of only 8 elements, where Si and O are in greatest abundance Most rocks and minerals that we see at the Earth’s surface are made of these 8 elements