Chapter 4 Flashcards
Matter is composed of ?
Atoms
Atom
smallest identifiable unit of an element
Element
a substance that cannot be broken down into simpler substances.
Democritus
if you divide matter into smaller and smaller pieces, you end up with tiny, indestructible particles.
Dalton atomic theory: Matter is composed of atoms.
- 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 shape
spherical
Thompson: PLUM PUDDING MODEL OF ATOM
An English physicist named J. J. Thomson (1856–1940) discovered a smaller and more fundamental particle called the electron.
Thompson Discovery in Depth:
Electrons are negatively charged.
Electrons are much smaller and lighter than atoms.
Electrons are uniformly present in many different kinds of substances.
He proposed that atoms must contain positive charge that balances the negative charge of electrons.
PLUM PUDDING MODEL OF ATOM
negatively charged electrons (yellow) were held in a sphere of positive charge (red).
Rutherford’s Gold Foil Experiment
Tiny particles called alpha-particles were directed at a thin sheet of gold foil. Most of the particles passed directly through the foil. A few, however, were deflected—some of them at sharp angles.
Nucleus
Most of the atom’s mass and all of its positive charge are contained in a small core
Electrons and protons
The number of negatively charged electrons outside the nucleus is equal to the number of positively charged particles (protons) inside the nucleus, so that the atom is electrically neutral.
Nucleus weight
The dense nucleus makes up more than 99.9% of the mass of the atom but occupies only a small fraction of its volume.
Electrons
The electrons are distributed through a much larger region but don’t have much mass.
Relative Size of the Proton and the Electron
If a proton had the mass of a baseball, an electron would have the mass of a rice grain.
The proton is nearly 2000 times as massive as an electron.
Electrical Charge Is a Property of Protons and Electrons
- Electrical charge is a fundamental property of protons and electrons.
- Positive and negative electrical charges attract each other.
- Positive–positive and negative–negative charges repel each other.
- Positive and negative charges cancel each other so that a proton and an electron, when paired, are charge-neutral.
The Properties of Protons, Neutrons, and Electrons
- Protons and neutrons have very similar masses.
- Electrons have almost negligible mass.
Electrical Storm Provides Evidence of Charge in Matter
-Matter is normally charge-neutral, having equal numbers of positive and negative charges that exactly cancel.
-In an electrical storm, the charge balance of matter is disturbed.
-The quick re-balancing of charge
often occurs in dramatic ways, such as is seen in
lightning.
How Atoms of the Elements Differ from One Another
Elements are defined by their numbers of protons.
It is the number of protons in the nucleus of an atom that identifies the atom as a particular element.
If an atom had a different number of protons, it would be a different element.
The number of protons in the nucleus of an atom is its atomic number and is given the symbol Z.
Atomic number
The number of protons in the nucleus of an atom
Additional elements with symbols based on their Greek or Latin names: Pb Hg Fe Ag Sn Cu
lead Pb plumbum mercury Hg hydrargyrum iron Fe ferrum silver Ag argentum tin Sn stannum copper Cu cuprum
elements were named after countries:
Polonium after Poland
Francium after France
Americium after the USA.
Curium is named after:
Marie Curie, a chemist who helped discover radioactivity and also discovered two new elements.
Dmitri Mendeleev
a Russian chemistry professor, proposed from observation that when the elements are arranged in order of increasing relative mass, certain sets of properties recur periodically.
Metals
- occupy the left side of the periodic table and have similar properties.
- good conductors of heat and electricity.
- tend to lose electrons when they undergo chemical changes.
Nonmetals
- occupy the upper right side of the periodic table.
- Nonmetals have more varied properties; some are solids at room temperature, while others are gases.
- As a whole, nonmetals tend to be poor conductors of heat and electricity.
- Nonmetals tend to gain electrons when they undergo chemical changes.
Metalloids
semiconductors because of their intermediate electrical conductivity, which can be changed and controlled.
Ions
atoms often lose or gain electrons to form charged particles called ions.
Cations
Positive ions
Anions
Negative ions
Charge of an ion location:
- shown in the upper right corner of the symbol.
- Ion charges are usually written with the magnitude of the charge first, followed by the sign of the charge.
Ion charge=
of protons—#of electrons
example Li+ ion with 3 protons and 2 electrons=
example F- ion with 9 protons and 10 electrons=
3-2=1+
9-10=1-
Isotopes
- Atoms with the same number of protons but different numbers of neutrons
- The number of neutrons in an isotope is the difference between the mass number and the atomic number.
Isotopes of neon:
Ne-21
Ne-22
Ne-20
The mass number (A) is :
the sum of the number of protons and the number of neutrons.
Atomic Mass: The Average Mass of an Element’s Atoms
(%/100amu) + (%/100amu) = ___ amu
Gallium has two naturally occurring isotopes: Ga-69, with mass 68.9256 amu and a natural abundance of 60.11%, and Ga-71, with mass 70.9247 amu and a natural abundance of 39.89%. Calculate the atomic mass of gallium.
- 11%/100= 0.6011
- 89%/100= 0.3989
(0. 601168.9256)+(0.398970.9247)=
69. 72304099
69. 72 amu
Radioactive Isotopes
The isotopes that emit few energetic subatomic particles from their nuclei and change into different isotopes of different elements.
