F13 quiz 1 condensed notes

shells of heavier chemical elements in a chemists

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: struct a crystal. In a crystal, countless unit cells are repeated in all directions of space. The crystal framework and chemical composition of a mineral together determine its physical properties. Matter in the universe, and indeed on Earth, is composed of chemical elements that are composed of identical atoms, the smallest units that retain the physical and chemical properties of the substance. Within each atom is a nucleus that contains subatomic particles called protons (electrical charge +1, atomic mass unit 1) and neutrons (electrically neutral, amu 1). Orbiting around the nucleus are electrons (negligible mass, electrical charge  ­1). Electrons may be visualized as occupying “shells,” or volumes of space surrounding an atomic nucleus. The innermost electron shell is fully occupied by 2 electrons; the next shell is fully occupied by 8 electrons, and so on for the third, fourth,... shells of heavier chemical elements. In a chemist’s terminology, an element’s atomic number equals the number of protons in the nucleus, so hydrogen (H) has one proton; helium (He) has two protons; uranium (U) has 92 protons, etc. The atomic mass of an atom is the sum of the protons and neutrons in the nucleus. Isotopes are atoms of an element with different numbers of neutrons, and are named by their atomic masses (ex. 235U which is pronounced uranium ­235). In a neutral atom, the numbers of protons and electrons are equal, but in an ion the atom has gained or lost electrons and become electrically charged. In the periodic table of the elements, elements are listed by their atomic numbers, starting with hydrogen (H), then helium (He), lithium (Li), beryllium (Be), and so on. The rows of the periodic table indicate the number of electron shells around the nuclei of atoms of that row, and the columns indicate the number of electrons in the outer shell of elements in that column. A chemical bond is a description of the forces that hold atoms together in a substance, and chemical bonding is a consequence of electron behavior. Consider the element sodium (Na) whose nucleus has 11 protons (positive charges). An electrically neutral Na atom would also have 11 electrons (negative) consisting of two filled inner shells (2 electrons, then 8 electrons) and an 11th electron, the beginning of the third shell. The element chlorine (Cl) lacks one electron to complete three electron shells. If Na donates its outermost electron to fill the “hole” in the Cl shell, the transfer makes both atoms more stable because their outermost shells are then filled. Gainin...
View Full Document

This document was uploaded on 03/03/2014 for the course GEO 303K at University of Texas.

Ask a homework question - tutors are online