Chapter 2 Flashcards
Dalton’s Atomic Theory (4 postulates)
- all matter is made up of tiny, indivisible particles called atoms. (NO LONGER CORRECT; protons, neutrons, and electrons)
- all atoms of a given element have the same mass and chemical properties and are different from atoms of another element.
- atoms of two or more different elements combine to form compounds. A particular compound is always made up of the same kinds of atoms that are in the same proportions.
- A chemical reaction involves rearrangement, separation, or combination of atoms. Atoms are never created or destroyed in a chemical reaction.
Law of Conservation of Mass
- Matter can be neither nor destroyed in a chemical reaction. (total mass of reactants before the reaction is always equal to the total mass of the products after the reaction)
Law of Definite Composition
- Any compound is always made up of elements in the same proportion by mass.
example:
The chemical formula of water particles is always made up of one O atom and two H atoms. The decomposition of 18.0 g. of H2O results in 16.0 g. of O atoms and 2 g. of H atoms, or an Oxygen:Hydrogen mass ration of:
mass ratio: (16.0 g. O ÷ 2.0 g. H) = (8.0 g. O ÷ 1.0 g. H) or 8 g. O: 1 g. H
Ratio hold true for any sample of pure water, regardless of its origin. Compounds have definite proportions of their constituent elements because the atoms that compose them, each with its own specific mass, occur in definite ratio. Since the ratio of atoms is the same for all samples of a particular compound, the ratio of masses is also the same.
Law of Multiple Proportions
- When 2 elements combine to form more than one compound, the different weights of one element that combine with the same weight of the other element are in a simple ratio of whole numbers.
example:
Carbon and Oxygen combine to form more than one compound. At the particulate level, Carbon and Oxygen atoms combine in a 1:1 ratio to form carbon monoxide/ CO. When they combine in a 1:2 ratio, carbon dioxide/CO2 is formed.
(a.) 1.0 g. carbon combines with 1.3 g. oxygen when CO is formed.
(b.) 1.0 g. of carbon combines with 2.6 g. oxygen when CO2 is formed. Thus, twice as many oxygen atoms combine with 1.0 g. of carbon in CO2 as compared to CO.
Plum Pudding Model of the Atom
- J.J. Thomson discovered even smaller and more fundamental particle called the electron
- found e- to be negatively charged, much smaller and lighter than atoms, and uniformly present in many different atoms
- discovery by using Cathode Ray Tube
- plum pudding model: e- uniformly distributed within positively charged sphere
The Gold Foil Experiment
- done by Ernest Rutherford
- directed beam of positively charged particles/ alpha particles at an ultra thin sheet of gold oil
Nuclear Model of the Atom
- most of atom’s mass and all of its positive charge contained in small core called nucleus
- most of volume of atom is empty space through which tiny e- are dispersed
- many negatively charged electrons outside the nucleus as there are positively charged particles (protons) inside the nucleus, so atom is electrically neutral
*scientists later found nucleus with p+ and n^0 and dense nucleus makes up more than 99.9% of mass of atom but occupies small fraction of volume (e- distributed through larger region, but not much mass)
Protons
- identifies element
- atoms contain same number of protons always belong to same element
Organization of Periodic Table (groups and periods)
- 18 groups/columns
(a.) elements in same group have similar chemical
properties
(b.) In US, A groups: main group/representative
elements and B groups include transition and inner
transition elements
(c.) Outside US, groups designated 1 to 18 - 7 periods/rows
- divided into metals, nonmetals, metalloids
Metals
- solid at room temp. (EXCEPT Hg)
- conduct heat and electricity
- usually ductile/drawn into wire
- malleable/rolled or stamped into sheet
- can form alloys (solution of 2 or more different metals)
- form cations (positively charged ions) when ionized by losing electrons
Nonmetals
- with exception of C in form of graphite, nonmetal do not conduct electricity
- form anions (negatively charged ions) when ionized by gaining electrons
Metalloids
- aka semimetals
- some physical characteristics of a metal but some chemical characteristics of a nonmetal
- include Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, Polonium, Astatine, Selenium
Alkali Metals
- group 1A metals (NOT include hydrogen)
- most reactive metals
- soft and shiny metals (softness increases going down column)
- good conductors of heat and electricity
- relatively low melting and boiling points
- form +1 ions
- react vigorously with H2O to form H2 gas and metal hydroxide (MOH)
- form compound with the halogens (group 7A elements) with the formula MX
- because very high reactivity, never found in pure state
Alkali Earth Metals
- group 2A metals
- very reactive metals but NOT as reactive as Group 1A elements
- also react with H2O to produce H2 gas and alkaline solutions EXCEPT Beryllium
- reactivity increases descending group
Halogens
- group 7A elements
- elements exist naturally as diatomic elements
- most reactive nonmetal elements
