Concepts of science chapter 8
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- Dalton
- (1766-1844)Hypothesized that for every chemical element there is a corresponding species of objects called atoms. this atom cannot be broken down any more.
- Molecule
- Any cluster of atoms that can be isolated
- electrolysis
- "splitting by electricity" allowed for rapid discovery of many elements.
- earth's composition
- 99% made of six elements: oxygen, silicon, magnesium, iron, aluminum, and calcium
- Rutherford's model of the atom
- a dense positively charged nucleus surrounded by oribiting cloud of negatively charged electrons
- other discoveries
-
for each proton in nucleus there is an electron in orb it thus electrical charges of an atom cancel out and the intact atom is neutral;
if an atom should gain or lose an electron this affects its overall charge; charged atoms are called ions. - ground state of atoms
- all electrons in lower energy level.
- excited state of atoms
- some or all electrons are in the highest energy levels
- photon
- in bohr model when an electron drops an energy level it emits energy(visible light)
- quantam leap
- an electron must disappear and reappear on another level without transversing the distance and with no time distance
- stars
- made mainly of two elements: hydrogen and helium
- living organisms
- 90% hydrogen carbon nitrogen oxygen phosphorus sulfur
- Thompson
- identified a subatomic particle called the electron, negatively charged
- Rutherford
- experimented with gold foil, proved existence of the nucleus
- electromagnetic radiation
- electrons don't fall into the nucleus
- Bohr
- said that electrons exist in various levels or shells located about the nucleus each shell corresponds to an energy level of the electron
- spectrum
- total collection of photons omitted by a given atom therefore each has a unique spectrum.
- emmission and absorption
- each element will emit and absorb light of the same wavelenght transparent or feflecting materials absorb specific wavelengths of light according to their atomic structure.
- spectroscopy
- study of elemental composition of materials by looking at absorption lines
- helium
- the elusive element, first found in suns light but not found on earth until 30 years later.
- laser
- light amplification by stimulated emission of radiation
- periodic table of elements
- elements arranged by their chemical properties.
- atomic number
- defines the sequence of elements in the table; number of protons in nucleus
- alkali metals
- first column- for example K,-Na)
- alkali earth metals
- second column (Mg, Ca)
- noble gases
- elements of the 8th column that do not form compounds readily
- atomic interaction
- explained by periodic table and bohr; when two atoms interact their outermost shell electrons dictate their interatctions and thus govern their bonding properties.
- metals
- most of the table is metals, conducts electricity well
- pauli exclusion principle
- no two electrons can occupy the same energy state(level and position in that level) at the same time.
- structure of electron shells
- there are naturally occurring spaces in the electron shells that can be filled by electrons as determined by spacing and electron spin
- shells
-
1st-2 spaces
2nd shell-8 spaces
3rd shell-8 spaces
4th- 18 spaces
5th-18 spaces
6th-32 spaces
7th(highest)-32 - rows
-
1-2 spaces
2-8 spaces
3-8 spaces
4-18 spaces
5-18 spaces
6-32 spaces
7-32 spaces - atomic mass
-
(atomic mass)=mp+mn
mass of atom is found by adding mass of each proton and each neutron present in the nucleus. - electrons in outer shell
- valence electrons
- chemical bonding
- commonly involves exchange or sharing of valence electrons
- valence-
- number of elctrons in the outer shell; also the combining power of atoms
- inert gases
- (noble gas) most stable arrangement of lowest energy because all shells are filled with electrons.
- quest of the atom
- to achieve the lowest energy state it can; so when atoms come near each other they may exchange or share electrons to achieve this state.
- chemical bond
- the result of redistribution of electrons that leads to a more stable configuration between two or more atoms
- strategies of atoms
-
give up electrons
gain electrons
share electrons - result of bonding
-
spontaneous- a release of energy
due to outside energy-may release or absorb energy - Atoms that are close to noble
-
1 less- H, F, Cl
1 more- Li, Na, K, Rb
tend to form ionic bonds - mettalic bonds
- bonds between metals; atoms float in a sea of electrons, many highly compressed gases can act as metal(O),
- alloy
- two or more metallic elements combined in a metalic bond.
- malleability
- a property of metals that allows atoms to rearrange themselves within the metallic bond to order to attain a new configuration in response to stresses; metals can be bent, shaped, molded due to this property.
- covalent bonds
- molecules that share electrons
- single bond
- one electron from each atom is shared
- the carbon bond
- the basic bond of all essential of molecules of life on earth. C atom config means it is equally likely to gain or lose 4 electrons
- the carbon-carbon system
- lower energy results from sharing of outer electrons with up to 4 other C atoms.
- organic chem
- study of C bonding and related bonding
- long chains of C and other atoms
- proteins, DNA, fats, cholesterol, etc.
- polar molecules
- molecules with either a positive or a negative side to them
- polarization
- electrons of neighbor atoms or molecules tend to be pushed away from a positive side of water; polarization makes substances like water act as a solvent(materials more easily disolves
- hydrogen bonds
- weak electrical attraction developed by the H atom itself after it is bonded to another element, like O or N
- Source of the force
- all charged parts of an atom exert electrical forces on all other neighbor atoms, so even if all atoms in a substance are electrically neutral and or non polar, the sum of the electrical charges within all atoms.
- gases
- collections of atoms or molecules that expands to take shape of and fill the volume available in a container
- atomic movement
- random bouncing off one another
- plasmas
- seas of electrically charged particles, properties can be confined by a magnetic field; conducts electricity; can grade into a gaseous state.
- liquids
- collections of atoms or molecules that have no fixed shape but maintain volume.
- water
- most common liquid on earth, but rare on other planets as far as we know.
- solids
- all materials that possess a more or less fixed ahpe and volume
- crystals
- groups of atoms that occur in a regularly repeating sequence farming a structure in which atoms or molecules occur in a regular and predictable way.
- unit cell
- the smallest subdivision of a crystal that shows the complete repeating pattern of atoms within the crystal.
- crystalline solids
-
composed of interlocking crystals
natural: rocks(such as granite)
man-made- alloys and ceramics
organic: teeth, bones - glass
- groups of atoms that are may be regular on a local scale, but are not regularly distributed throughout the solid.
- polymers
- long and large molecules that are formed from numerous smaller molecules; regular pattern of atoms in one direction
- plastics
- made of intertwined polymers derived from petroleum
- liquid crystals
- an odd intermediate state of matter that is half way between liquid and crystalline solid- man made
- changes of state in matter
- freezing and melting- changes between liquid and solid
- boiling and condensation
- changes between liquid and gas
- sublimation
- change from solid to gas
- driving force: temp
- transitions result from temp changes
- chemical reactions
-
atoms and molecules coming together to form larger structure or larger structures breaking apart
reactants goes to products - exothermic
- reactions that give off energy wile it occurs. when atoms or molecules combine the total energy is less, heat or light is given off
- endothermic
- reactions that take in energy while it occurs; when atoms or molecules combine the total energy is more so energy is absorbed
- oxidation
- giving up e- to oxygen
- combustion
- rapid oxidation reaction
- reduction
- chemical reaction in which electrons are transferred to an atom from other elements
- smelting
-
reducting iron by heating in the presence of CO to make
F +CO2 - precipitation
- solids forming as a liquid evaporates or due to saturation in the liquid by a dissolved compound
- solution
- dissolving of solids into a liquid to dispered ions in a solution
- acid
- any material that when put in water produces positivly charged H ions in the solution
- base
- any material that when put in water produces negatively charged OH- ions
- acid-based reaction
- when two are brought together, water is formed
- acid and base with pH
- below 7 on ph scale base is above 7