Chapter 2 Flashcards
Who were the first to try to explain why chemical changes occur and described matter?
Greeks
Who discovered several elements & learned to prepare the mineral acids?
Alchemists
Who created the foundations of modern chemistry in 1400s-1500s?
Georg Baur; Paracelsus
First chemist to perform truly quantitative experiments
Robert Boyle
Who said “phlogiston” flows out of burning material? Who discovered oxygen gas?
Stahl; Joseph Priestley
Who explained nature of combustion & carefully weighed reactants & products?
Antoine Lavoisier
Define law of conservation of mass
Mass is neither created nor destroyed
Lavoisier showed combustion involved __ & life is supported by it
Oxygen
Who found that copper carbonate is always 5.3 parts Cu, 4 parts O, 1 part C by mass?
Joseph Proust
Define law of definite proportion
A given compound always contains exactly the same proportion of elements by mass
Dalton said if elements have ___, compounds always have the __ __ of atoms
Particles; Same combination
Define law of multiple proportions
When 2 elements form a series of compounds, the ratios of the masses of the second element that combine with 1g of the first element can always be reduced to small whole numbers
Describe Dalton’s theory (4)
1) each element is made up of tiny particles called atoms 2) atoms of a given element are identical; the atoms of different elements are different in some way3) chemical compounds are formed when atoms of different elements combine with each other; a given compound always has the same relative numbers & types of atoms4) chemical reactions involve reorganization of the atoms- changes in the way they are bound together; the atoms are not changed in a chemical reaction
Define atomic mass (atomic weights)
The weighted average mass of the atoms in a naturally occurring element
Who developed the modern symbols for elements used in writing formulas?
Berzelius
Describe Avogadro’s hypothesis
At the same temperature & pressure, equal volumes of different gases contain the same number of particles
1860: who found the correct atomic mass of carbon is 12?
Cannizzaro
Describe JJ Thompson’s experiments
Studied electrical discharges in cathode-ray tubes; found when high voltage was applied to the tube, a cathode ray was produced; ray was a stream of electrons
Define cathode rays
Ray emanating from the negative electrode (cathode) in a partially evacuated tube; a stream of electrons
What did Thompson postulate about the atom?
An atom consists of a diffuse cloud of positive charge with negative electrons embedded randomly in it, which created the plum pudding model of the atom
Define electrons
Negatively charged particle that moves around the nucleus of an atom
Define radioactivity
The spontaneous decomposition of a nucleus to form a different nucleus
Three types of radioactive emission
Gamma rays; Beta particles; Alpha particles
Define gamma ray; Define beta particle; Define alpha particle
High-energy “light”; High-speed electron; 2+ charge
Define nucleus
Small, dense center of positive charge in an atom
What did Rutherford discover?
Metal-foil experiment: shot alpha particles at thin foil, some particles deflected (caused by a center of concentrated positive charge containing most of the mass
Define nuclear atom
Atom with a dense center of positive charge with electrons moving around the nucleus at a distance that is large relative to the nuclear radius
Mass of electron; Mass of proton & neutron
9.11 • 10^-31 kg; 1.67 • 10^-27 kg
Define proton
Positively charged particle in an atomic nucleus
Define neutron
Particle in the nucleus with the same mass as a proton with no charge
The nucleus is almost all of an atom’s __; electrons constitute most of the atomic __
Mass; Volume
__ affect interactions with other atoms; atoms of different __ have different chemical behavior; number of __ must equal number of __ to have no net charge
Electrons; Elements; Electrons; Protons