Chapter 1: Atoms Flashcards
anion
A negatively charged ion.
atomic mass
The average mass in amu of the atoms of a particular element based on the relative abundance of the various isotopes; it is numerically equivalent to the mass in grams of one mole of the element. Weighed according to the natural abundance of each isotope. Sometimes called atomic weight or standard atomic weight.
= Σ(fraction of isotope n) X (mass of isotope n)
atomic mass unit (amu)
A unit used to express the masses of atoms and subatomic particles; defined as 1/12 the mass of a carbon atom containing 6 protons and 6 neutrons. The mass of a proton or neutron is approximately 1 amu.
atomic number (Z)
The number of protons in an atom; the atomic number defines the element.
atomic theory
Proposed by English chemist John Dalton.
- Each element is composed of tiny, indestructible particles called atoms.
- All atoms of a given element have the same mass and other properties that distinguish them from the atoms of other elements.
- Atoms combine in simple, whole-number ratios to form compounds.
- Atoms of one element cannot change into atoms of another element. In a chemical reaction, atoms only change the way that they are bound together with other atoms.
atoms
A submicroscopic particle that constitutes the fundamental building block of ordinary matter; the smallest identifiable unit of an element.
(A water molecule is composed of 3 atoms, 1 oxygen and 2 hydrogen atoms.)
cathode ray
A stream of electrons produced when a high electrical voltage is applied between two electrodes within a partially evacuated tube.
cathode ray tube
A partially evacuated tube equipped with electrodes to produce cathode rays.
cation
A positively charged ion.
chemical reaction
A process by which one or more substances are converted to one or more different substances; see also chemical change.
Matter is neither created, nor destroyed.
chemistry
The science that seeks to understand the properties of matter by studying the structure of the particles that compose matter.
chemical symbol
A one- or two-letter abbreviation listed directly below its atomic number on the periodic table.
composition
Classification of matter where it depends on the types of particles. (Whether there is only one type or more than one type.)
compound
A substance composed of two or more elements in fixed, definite proportions.
i.e.: water
electrical charge
A fundamental property of certain particles that causes them to experience a force in the presence of electrical fields.
electron
A negatively charged, low-mass particle found outside the nucleus of all atoms that occupies most of the atom’s volume but contributes almost none of its mass.
element
A substance that cannot be chemically broken down into simpler substances.
[Helium]
experiments
A highly controlled procedure designed to generate observations that may support a hypotheses or prove it wrong. Can lead to development of scientific law.
gas
the state of matter in which atoms or molecules have a great deal of space between them and are free to move relative to one another; lacking a definite shape or volume, a gas conforms to the shape and volume of its container.
heterogenous mixture
A mixture in which the composition varies from one region to another.
[Wet sand: Two types of particles that separate into distinct regions.]
hypothesis
A tentative interpretation or explanation of an observation.
A good hypothesis is falsifiable, which means that it makes predictions that can be confirmed or refuted by further observations.
International System of Units
The standard unit system used by scientists; based on the metric system.
ions
An atom or molecule with a net charge caused by the loss or gain of electrons.
homogeneous mixture
A mixture with the same composition throughout.
[Tea with sugar: Two types of particles that thoroughly mix]
isotope
One of two or more atoms of the same element with the same number of protons but different numbers of neutrons and consequently different masses.
law of conservation of mass
The law stating that matter is neither created nor destroyed in a chemical reaction.
law of multiple proportions
The law stating that when two elements (A and B) form two different compounds, the masses of element B that combine with one gram of element A can be expressed as a ratio of small whole numbers.
law of definite proportions
The law stating that all samples of a given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements.
mass number
(A); The sum of the number of protons and neutrons in an atom.
liquid
The state of matter in which atoms or molecules pack about as closely as they do in solid matter but are free to move relative to each other, resulting in a fixed volume but not a fixed shape.
mass spectrometry
An experimental method of determining the precise mass and relative abundance of isotopes in a given sample using an instrument called a mass spectrometer.
matter
Anything that occupies space and has mass. It is particulate – it is composed of particles.
metric system
The system of measurements used in most countries in which the meter is the unit of length, the kilogram is the unit of mass, and the second is the unit of time.
mixture
A substance composed of two or more different types of atoms or molecules that can be combined in variable proportions.
Sweet tea, wet sand
molecule
Two or more atoms joined chemically in a specific geometrical arrangement.
natural abundance
The relative percentage of a particular isotope in a naturally occuring sample with respect to other isotopes of the same element.
neutron
An electrically neutral subatomic particle found in the nucleus of an atom, with a mass almost equal to that of a proton.
nuclear theory
The theory that most of the atom’s mass and all of its positive charge are contained in a small, dense nucleus.
nucleus
The very small, dense core of the atom that contains most of the atom’s mass and all of its positive charge; the nucleus is composed of protons and neutrons.
periodic table
A table that arranges all known elements in order of increasing atomic number; elements with similar properties generally fall into columns on the periodic table.
proton
A positively charged subatomic particle found in the nucleus of an atom.
pure substance
Made up of only one type of particle (one component), and its composition is invariant (it does not vary from one sample to another). Individual atoms or groups of atoms joined together.
helium, water, table sale (NaCl)
radioactivity
The emission of subatomic particles or high-energy electromagnetic radiation by the unstable nuclei of certain atoms.
scientific law
A brief statement or equation that summarizes past observations and predicts future ones.
It decribes how nature behaves – they are generalizations about what nature does.
solid
A state of matter in which atoms or molecules are packed close to one another in fixed locations with definite volume.
state
A classification of a form of matter as a solid, liquid, or gas. It depends on the relative positions of the particles and how strongly they interact with one another (relative to temperature).
substance
A specific instance of matter – such as air, water, or sand.
theory
A proposed explanation for observations and laws, based on well-established and tested hypothesis; a theory presents a model of the way nature works and predicts behavior beyond the observations and laws on which it was based.
unit
A standard quantity used to specify measurements. To assign a number to an observation.
