[NOTES] Chapter 2: The Components of Matter Flashcards
Element
The simplest type of matter with unique physical and chemical properties
Atom
The smallest unit of an element that retains its chemical nature
Compound
Consists of two or more different elements that are bonded chemically
- elements are present in fixed parts by mass (fixed mass ratio) because each unit of a compound consists of a fixed number of atoms of each element
- a compound’s properties are different from the properties of its elements
Mixture
Consists of two or more substances (elements and/or compounds that are physically intermingled, not chemically combined
Law of Mass Conservation
The total mass of substances does not change during a chemical reaction
- mass cannot be created nor destroyed
Law of Definite (or constant) Composition
No matter what its sourced, a particular compound is composed of the same elements in the same parts (fractions) by mass
Fraction by Mass (Mass Fraction)
The part of the compound’s mass that each element contributes
- mass fraction = (mass of element X in compound A) / mass of compound A
Percent by Mass (Mass percent, mass %)
The fraction by mass expressed as a percentage (multiplied by 100)
- mass percent = mass friction x 100
Postulates of the Atomic Theory
- All matter consists of atoms
- Atoms of one element cannot be converted into atoms of another element
- Atoms of an element are identical in mass and other properties and are different from atoms of any other element
- Compounds result from the chemical combination of a specific ratio of atoms of different elements
Mass Conservation
Atoms cannot be created or destroyed (P1) or converted into other types of atoms (P2), therefore, a chemical reaction cannot possibly result in a mass change because atoms are just combined differently
Definite Composition
A compound is a combination of a specific ratio of different atoms (P4), each of which has a particular mass (P3), thus, each element in a compound must constitute a fixed fraction of the total mass
Multiple Proportions
Atoms of an element have the same mass (P3) and are indivisible (P1). The masses of element B that combine with a fixed mass of element A must give a small, whole-number ratio because different numbers of B atoms combine with each A atom in different compounds
Cathode Rays
Originated at the negative electrode (cathode) and moved to the positive electrode (anode)
- ex. when the electric power source was turned on, a “ray” could be seen striking the phosphor-coated end of the tube, which emitted a glowing spot of light
Ernest Rutherford’s Conclusion
Alpha particles were being repelled by something small, dense, and positive; he found
- an atom is mostly space occupied by electrons
- the center contains a tiny region called the “nucleus”, that contains all the positive charge and essentially all the mass of the atom
Proton (p^+)
Positive charge in the nucleus, 1+
Neutron (n^0)
No charge, in the nucleus
- mass of proton or neutron is nearly 2000x the mass of an electron
Electron (e^-)
Negative charge, 1-
- an atom is neutral because the number of protons in the nucleus equals the number of electrons surrounding the nucleus
Atomic Number (Z)
Equals the number of protons in the nucleus of each of its atoms
- all atoms of an element have the same atomic number, and the atomic number of each element is different from that of any other element
Mass Number (AO
The total number of protons and neutrons in the nucleus of an atom
- each proton and each neutron contributes one unit to the mass number
Atomic (Element) Symbol
Element name based on its English, Latin, or Greek name
Isotopes
Atoms that have different numbers of neutrons and therefore different mass numbers
- most elements occur in nature in a particular isotopic composition, which specifies the proportional abundance of each of its isotopes
Atomic Mass Unit (amu)
A measurement relative to the mass of an atomic standard (carbon-12 atom), therefor the amu is 1/12 the mass of a carbon-12 atom
- the unit has, however, been changed to the dalton (Da)
Mass Spectrometry
A method for measuring the relative masses and abundances of atomic-scale particles very precisely
Periodic Table of the Elements
Based on Mendeleev’s version (but arranged by atomic number, not mass), is one of the great classifying schemes in science and an indispensable tool
- boxes are arranged into a grid of periods (horizontal rows) and groups (vertical columns)
