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the first to try to explain why chemical changes occur. 4 fundamental substances- fire, earth, water, and air. also considered whether matter is continuous. democritus said it is made up of small individual units of particles and called these atamos (atoms). but had no proof of their ideas
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the first to try to explain why chemical changes occur. 4 fundamental substances- fire, earth, water, and air. also considered whether matter is continuous. democritus said it is made up of small individual units of particles and called these atamos (atoms). but had no proof of their ideas
Robert Boyle, 1661
first to perform truly quantitative experiments. he said there has to be more than 4 elements, and anything was an element unless it could be broke down into two or more simpler substances
mass is neither created nor destroyed- conservation of mass
law of definite proportions- a given compound always contains exactly the same proportion of elements by mass (ex: water is always going to be 11% H and 89% 0 by mass)
stimulated dalton to think about atoms. 1. elements are composed of atoms. 2. atoms of a given element are identical. 3. compounds are composed of more than one element/when atoms combine with each other, and the ratio of the number of atoms of any 2 elements in a given compound equals an integer or simple fraction. 4. chemical reactions are reorganizations of atoms
expanded on proust's law of definite proportions and made the law of multiple proportions- when 2 elements form a series of compounds, then the ratio of the mass of 1 element to a fixed ratio of the other element can always be reduced to simple fractions/small whole numbers
JJ Thomson- Plum Pudding Model (1898)
studied electrical discharges in cathode-ray tubes. when a high voltage was applied, a 'ray' of negatively charged particles was produced, now called electrons. proposed that ALL atoms must contain electrons, but atoms are neutral, so there must be a positive charge too. postulated that an atom consisted of diffude cloud of positive charge with neg. electrons embedded randomly in it
tested the plum pudding model. directed alpha particles at a thin sheet of metal foil. expected them to travel through with minor deflections. most passed through but many were deflected at large angles. this could only be caused by a center of concetrated positive charge that contains most of the atom's mass- nucleus with electrons moving around it
Modern views of atomic structure- the atom
consists of a tiny nucleus with a diameter of about 10 to the -13 cm, and electrons that move about the nucleus at an average distance of about 10 to the -8 cm away from it. the chemistry of an atom arises from its electrons
contains protons (positive charge) and neutrons (no charge). the nucleus is very small compared with the overall size of the atom and has an extremely high density; it accounts for almost all of the atom's mass
the number and arrangement of electrons accounts for different chemical properties of different atoms. the number of electrons possessed by an atom greatly affects its ability to interact with other atoms. the number of electrons MUST EQUAL THE NUMBER OF PROTONS
atoms with the same number of protons but different numbers of neutrons
Atomic number
number of protons (subscript)
Mass number
TOTAL number of protons and neutrons (superscript)
Chemical bonds
forces that hold atoms together
Covalent bonds
one way that atoms can form bonds is by SHARING ELECTRONS
aggregate of at least 2 atoms in a definite arrangement held together by a chemical bond
atom or molecule with a net positive or negative charge (losing or adding electrons)
negative ion
positive ion
Ionic bonds
because anions and cations have opposite charges, they attract each other. this force of attraction between oppositely charged ions is ionic
Metal atoms
tend to LOSE electrons to form positive ions
tend to GAIN electrons to form anions in reactions with metals. often bond to each other by forming COVALENT bonds
Groups/families in the periodic table
same VERTICAL columns and have similar chemical properties
HORIZONTAL rows of elements
Binary compounds (type 1, ionic)
contain a cation, always written FIRST in the formula, and an anion. a one atom cation takes its name from the name of the element. the anion is named by taking the first part of the element name and adding IDE. (sodium chloride)
Binary compounds (type 2, ionic)
the charge on the metal ion must be specified; the roman numeral indicates the charge of the cation
Binary compounds (type 3, covalent)
contains two NON metals, do not contain ions. the first element is named first, using the full element name. the second is named as if it were an anion. PREFIXES used to denote the number of atoms present. mono is never used for naming the first element
a molecule with one or more H+ ions attached to an anion
Anions NOT containing oxygen
the acid is named with the prefix HYDRO and the suffix -IC
Anions containing oxygen
the acid name is formed from the root name of the anion with a suffix of -IC or -OUS
-IC ending
if the anion name ends in -ATE
-OUS ending
if the anion name ends in -ITE
Mass spectrometer
compares the masses of atoms
Mole/Avogadro's number
use in counting atoms. the number equal to the number of carbon atoms in exactly 12 grams of pure 12C. 6.022x10 to the 23rd= 1 mole. an element's mass expressed in grams is equal to 1 mole
Molar mass/molecular weight
the mass in grams of 1 mole of a compound

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