Chapter 1: Atoms Flashcards
How are the properties of matter determined?
By the structure of the atoms and molecules that compose it. A small change in structure, such as a different shape, results in a significant change in properties.
Define matter.
Anything that occupies space and has mass.
Define atoms.
A submicroscopic particle that constitutes the fundamental building block of ordinary matter; the smallest identifiable unit of an element.
Define molecules.
Two or more atoms joined chemically in a specific geometrical arrangement.
Define chemistry.
The science that seeks to understand the properties of matter by studying the structure of the particles that compose matter.
Define substance.
A specific instance of matter, such as air, water, or sand.
Define state.
A classification of a form of matter as a solid, liquid, or gas.
How is the state of matter classified?
It depends on the relative positions of the particles and how strongly they interact with one another (relative to temperature).
How is matter classified?
By its state or by its composition.
Define composition.
Refers to the type of particles that compose matter; by composition is one way to classify matter.
Define solid.
Particles that compose solid matter attract one another strongly and therefore pack closely to each other in fixed locations. Although the particles vibrate, they do not move around or past each other. Fixed volume and rigid shape.
Define liquid.
The particles that compose liquid matter pack about as closely as particles do in solid matter, but slightly weaker attractions between the particles allow them to move relative to each other, giving liquids a fixed volume but not a fixed shape. Liquids assume the shape of their container.
Define gas.
The particles that compose gaseous matter attract each other only very weakly - so weakly that they do not clump together as particles do in a liquid or solid. Instead, the particles are free to move large distances before colliding with one another. Gases always assume the shape and volume of their container.
What state of matter can be compressed?
Gases, because there is so much empty space between atoms or molecules in the gaseous state.
Define pure substance.
A substance made up of only one type of atom or molecule, and its composition is invariant.
Define mixture.
A substance composed of two or more different types of atoms or molecules that can be combined in variable proportions.
Define element.
A substance that cannot be chemically broken down into simpler substances.
Define compound.
A substance composed of two or more elements in fixed, definite proportions.
Define heterogenous mixture.
A mixture in which the composition varies from one region to another.
Define homogeneous mixture.
A mixture with the same composition throughout.
Define hypothesis.
A tentative interpretation or explanation of an observation. A good hypothesis is falsifiable.
Define experiment.
A highly controlled procedure designed to generate observations that may support a hypothesis or prove it wrong.
Define scientific law.
A brief statement or equation that summarizes past observations and predicts future ones.
Define law of conservation of mass.
The law stating that matter is neither created nor destroyed in a chemical reaction.
Define theory.
A proposed explanation for observations and laws, based on well-established and tested hypotheses; a theory presents a model of the way nature works and predicts behavior beyond the observations and laws on which it was based.
Who proposed the atomic theory?
John Dalton
What laws led to the development of the atomic theory?
- law of conservation of mass
- law of definite proportions
- law of multiple proportions
Define chemical reaction.
A process in which one or more substances are converted to one or more different substances.
Who proposed the law of conservation of mass?
Antoine Lavoisier
Who proposed the law of definite proportions?
Joseph Proust
Define law of definite proportions.
The law stating that all samples of a given compound have the same proportions of their constituent elements.
Who proposed the law of multiple proportions?
John Dalton
Define 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.
Define atomic theory.
The theory that each element is composed of tiny indestructible particles called atoms, that all atoms of a given element have the same mass and other properties, and that atoms combine in simple, whole-number ratios to form compounds.
Define cathode rays.
A stream of electrons produced when a high electrical voltage is applied between two electrodes within a partially evacuated tube.
How do particles travel in a cathode ray tube?
The beam of particles, called cathode rays, travel from the negatively charge electrode (cathode) to the positively charged one (anode).
Define electrical charge.
A fundamental property of certain particles that causes them to experience a force in the presence of electric fields.
What did J.J Thomson discover?
Discovered the electron; measured the charge-to-mass ratio of the cathode ray particles by deflecting them using electric and magnetic fields. The value he measured (-1.76x10^8 coulombs/gram) implied that the cathode ray particle was about 2000 times lighter than hydrogen (the lightest known atom).
Define 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.
What did Robert Millikan discover?
The charge of a single electron; calculated the charge on oil droplets falling in an electric field, which was always a whole-number multiple of -1.60218 x 10^-19 C, or the charge of a single electron.
How did J.J. Thomson describe the structure of an atom?
Plum-pudding model; he proposed that the negatively charged electrons were small particles held within a positively charged sphere.
Define radioactivity.
The emission of subatomic particles or high-energy electromagnetic radiation by the unstable nuclei of certain atoms.
What are three types of radioactivity?
alpha particles, beta particles, and gamma rays
How do alpha particles compare to other forms of radioactivity?
They are positively charged and by far the most massive.
What did Ernest Rutherford discover?
The nuclear theory model of the atom; shot alpha particles at an ultrathin sheet of gold foil. Most particles passed through, but some were deflected and some even bounced back. Concluded that the mass and positive charge must be concentrated in a space much smaller than the size of the atom itself.
Define nuclear theory.
The theory that most of the atom’s mass and all of its positive charge are contained in a small, dense nucleus. Most of the volume of the atom is empty space, throughout which electrons are dispersed. There are as many negatively charged electrons outside the nucleus as there are positively charged particles within the nucleus.
Define 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.
Define protons.
A positively charged subatomic particle found in the nucleus of an atom.
What did James Chadwick discover?
The neutron
Define neutrons.
An electrically neutral subatomic particle found in the nucleus of an atom, with a mass almost equal to that of a proton.
What is the mass of a proton?
1.67262 x 10^-27 kg = 1.00727 amu
What is the mass of a neutron?
1.67493 x 10^-27 kg = 1.00866 amu
Define 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.
What is the mass of an electron?
0.00091 x 10^-27 kg = 0.00055 amu
Define atomic number (Z).
The number of protons in an atom; the atomic number defines the element.
Define periodic table.
The table that arranges all known elements in order of increasing atomic number; elements with similar properties generally fall into columns on the periodic table.
Define chemical symbol.
A one- or two- letter abbreviation for an element that is listed directly below its atomic number on the periodic table.
Define isotopes.
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.
Define natural abundance.
The relative percentage of a particular isotope in a naturally occurring sample with respect to other isotopes of the same element.
Define mass number (A).
The sum of protons and neutrons in an atom.
Define ions.
An atom or molecule with a net charge caused by the loss or gain of electrons.
Define cations.
A positively charged ion.
Define anions.
A negatively charged ion.
Define atomic mass.
(atomic weight) The average mass in amu of the atoms of a particular element based on the relative abundance of the various isotopes; numerically equivalent to the mass in grams of one mole of the element.
Formula atomic mass.
atomic mass = Σ (fraction of isotope) x (mass of isotope)
Define 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.
Define mole (mol).
A unit defined as the amount of material containing 6.0221421 x 10^23 particles.
Define Avogadro’s number.
The number of C-12 atoms in exactly 12g of C-12 equal to 6.0221421 x 10^23
Define molar mass.
The mass in grams of one mole of atoms of an element; numerically equivalent to the atomic mass of the element in amu.
