Chemistry Chapter 3
Democritus
400BC Greek thinker
atom- nature’s basic particle
Aristotle
generation succeeding Democritus
didn't believe in atoms
all matter is continuous
element- substance that cannot be further broken down by chemically/ordinary means
elements combine to form compounds
different chemical/physical propertied than the elements that make them up
chemical reaction- transformation of a substance to a new substance
law of conservation of mass- mass is neither created nor destroyed during ordinary chemical reaction or physical change
law of definite proportions- chemical compound contains same elements in same proportions by mass regardless of the size of the sample or source of the compound
**law of multiple proportions-**if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always the ratio of small whole numbers
proposed explanation for law of conservation of mass, definite proportions, and multiple proportions- his 5 postulates
5 Postulates:
all matter is composed of extremely small particles called atoms
atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, other propertied
atoms cannot be subdivided, created, destroyed
atoms of different elements combine in simple whole-number ratios to form chemical compounds
in chemical reactions, atoms are combined, separated, or rearranged
not all aspects of Dalton’s theory have been proven correct
atoms can be divided into smaller parts
although law of conservation of mass still holds true
a given element can have atoms with different masses
Dalton’s theory has been modified
modern atomic theory concepts:
all matter is composed of atoms
atoms of any one element differ in properties from atoms of another element remain unchanged
atom- smallest particle of an element that retains the chemical properties of that element
two regions of an atom:
nucleus- small region in the center
at least one proton- positive charge
at least one neutron- neutral charge
area around nucleus occupied by electrons- negatively charge particles
subatomic particles- proton, electron, neutron
current passing through cathode tube causes it to glow
observations lead to hypothesis- particles were negatively charged
experiments support: Thompson measure ratio of particles to mass
always the same
cathode rays composed of identical negative charge particles- electrons
electrons in all atoms
atoms are divisible
large charge to mass ratio
atoms are electrically neutral
must have a positive
electrons have much less mass than atoms, so other particles must have much more mass
plum pudding model- electrons evenly spread throughout and the rest is negative
Ernest Rutherford- shoot positive alpha particles at think gold foil
some deflect
must be hitting something positive and dense in the center- nucleus
Bhor- propose atomic model
electrons surround positive nucleus like planets around the sun
atomic nuclei made of protons and neutrons
protons= positive charge, electrons= negative charge
equal in magnitude
atoms are electrically neutral: same number of protons and electrons
atoms of different elements have different numbers of protons- affects positive charge
protons determine identity of an atom
nuclear forces: the interaction that binds protons and neutrons, protons and protons, and neutrons and neutrons together in a nucleus
usually particles with the same charge repel each other, but the particles are so close that a strong attraction is formed
electron cloud: region outside of the nucleus where electrons are stored
radius of an atom- from the center of the nucleus to the outer portion of the electron cloud
extremely small
measured in picometer (pm)
atomic number: the number of protons in each atom of an element
identifies the element because different elements have different atomic numbers
atoms are neutral, so the atomic number also tell the number of electrons
isotopes: atoms of the same element with different masses
same number of protons and electrons but different number of neutrons
mass number: total number of protons and neutrons that make up the nucleus of an isotope
identified by specifying the mass number
2 methods:
hyphen notation
mass number written with a hyphen after the element name
Hydrogen-3
nuclear symbol
shows composition of the nucleus
superscript= mass number
subscript= atomic number
32 He
Democritus
400BC Greek thinker
atom- nature’s basic particle
Aristotle
generation succeeding Democritus
didn't believe in atoms
all matter is continuous
element- substance that cannot be further broken down by chemically/ordinary means
elements combine to form compounds
different chemical/physical propertied than the elements that make them up
chemical reaction- transformation of a substance to a new substance
law of conservation of mass- mass is neither created nor destroyed during ordinary chemical reaction or physical change
law of definite proportions- chemical compound contains same elements in same proportions by mass regardless of the size of the sample or source of the compound
**law of multiple proportions-**if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always the ratio of small whole numbers
proposed explanation for law of conservation of mass, definite proportions, and multiple proportions- his 5 postulates
5 Postulates:
all matter is composed of extremely small particles called atoms
atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, other propertied
atoms cannot be subdivided, created, destroyed
atoms of different elements combine in simple whole-number ratios to form chemical compounds
in chemical reactions, atoms are combined, separated, or rearranged
not all aspects of Dalton’s theory have been proven correct
atoms can be divided into smaller parts
although law of conservation of mass still holds true
a given element can have atoms with different masses
Dalton’s theory has been modified
modern atomic theory concepts:
all matter is composed of atoms
atoms of any one element differ in properties from atoms of another element remain unchanged
atom- smallest particle of an element that retains the chemical properties of that element
two regions of an atom:
nucleus- small region in the center
at least one proton- positive charge
at least one neutron- neutral charge
area around nucleus occupied by electrons- negatively charge particles
subatomic particles- proton, electron, neutron
current passing through cathode tube causes it to glow
observations lead to hypothesis- particles were negatively charged
experiments support: Thompson measure ratio of particles to mass
always the same
cathode rays composed of identical negative charge particles- electrons
electrons in all atoms
atoms are divisible
large charge to mass ratio
atoms are electrically neutral
must have a positive
electrons have much less mass than atoms, so other particles must have much more mass
plum pudding model- electrons evenly spread throughout and the rest is negative
Ernest Rutherford- shoot positive alpha particles at think gold foil
some deflect
must be hitting something positive and dense in the center- nucleus
Bhor- propose atomic model
electrons surround positive nucleus like planets around the sun
atomic nuclei made of protons and neutrons
protons= positive charge, electrons= negative charge
equal in magnitude
atoms are electrically neutral: same number of protons and electrons
atoms of different elements have different numbers of protons- affects positive charge
protons determine identity of an atom
nuclear forces: the interaction that binds protons and neutrons, protons and protons, and neutrons and neutrons together in a nucleus
usually particles with the same charge repel each other, but the particles are so close that a strong attraction is formed
electron cloud: region outside of the nucleus where electrons are stored
radius of an atom- from the center of the nucleus to the outer portion of the electron cloud
extremely small
measured in picometer (pm)
atomic number: the number of protons in each atom of an element
identifies the element because different elements have different atomic numbers
atoms are neutral, so the atomic number also tell the number of electrons
isotopes: atoms of the same element with different masses
same number of protons and electrons but different number of neutrons
mass number: total number of protons and neutrons that make up the nucleus of an isotope
identified by specifying the mass number
2 methods:
hyphen notation
mass number written with a hyphen after the element name
Hydrogen-3
nuclear symbol
shows composition of the nucleus
superscript= mass number
subscript= atomic number
32 He