Chapter 2 - Atoms, Ions, Molecules Flashcards
Atomic Symbol
Used to represent an atom corresponding to a particular element
Dalton’s Atomic Theory
- 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 atoms of other elements
- Atoms combine simple, whole-number ratios to form molecules of compounds
- In a chemical reaction, atoms of one element cannot change into atoms of another element. They simply rearrange the way they are attached
Subatomic Particles of Atoms and their Charges
Protons(+)
Electrons(-)
Neutrons(neutral)
Rutherford’s Model of Atomic Structures
Atom = dense, heavy nucleus at center
Nucleus contains protons and neutrons (both make up nearly entire mass of atom)
Nucleus surrounded by electron cloud
JJ Thomson (1856-1940)
Discovered electrons in 1897 using a cathode-ray tube
Cathode-Ray Tube
Consists of glass tube where most if the air was removed.
Used by JJ Thomson to discover electrons
Plum Pudding Model (of atom)
Idea of a positively charged nucleus and the negatively charged electrons distributed throughout the positively charged sphere
Robert Millikan (1868-1953)
Determines the charge of electron through oil drop experiment
Henri Becquerel (1896)
Discovered radioactivity
Noticed that some materials produced invisible radiation consisting of charged particles
Radioactivity
Spontaneous emission of high energy radiation particles (beta, alpha particles)
Beta Particles (B)
High energy electrons (negatively charged)
Alpha Particles (a)
Positively charged (+2) Mass= He nucleus
Atomic Mass Unit (amu)
Unit used to express relative masses of atoms and subatomic particles
1amu = 1/12 of carbon atom
(Carbon made up of 6protons 6neutrons)
1amu = 1 Dalton (Da)
Dalton (Da)
1 Da = 1 amu
Francis W. Aston (1877-1945)
Used charged beam of neon (Ne+) and noticed 2 signals which meant 2 different isotopes
Discovered isotopes
Isotopes
Atoms of an element containing the same number of protons but different neurons
Ex. neon
1 isotope has 10 neutrons in it’s nucleus and a mass of 20amu
Another isotope has 12 neutrons and a mass of 22amu (protons remain the same)
Nuclides
Each individual isotope with a particular combo of protons and neutrons
Atomic Number
Number of protons in the nucleus
Determines identity of element
Atomic Mass Number
Total number of nucleons (protons & neutrons) in nucleus
Average Atomic Mass
Weighted average of masses of all isotopes of an element
Calculated by multiplying natural abundance by its mass (im amu) and then summing these products
Natural Abundance
Proportion of a particular isotope; usually expressed as a percentage relative to all isotopes for that element
(How much of each isotope exists in relative to the other isotopes existing for that element)
Only non-decaying stable isotopes occur naturally and therefore have natural abundance
Dimitri Mendeleev (1834-1907)
1872 - published a periodic table
Ordered elements by increasing atomic mass (in modern: ordered by atomic numbers)
Arranged elements in columns based on similar chemical & physical properties
Left open spaces for elements not yet discovered
Based on the locations of the empty cells he was able to predict the chemical and physical properties
Modern Period Table
Elements classified according to physical and chemical properties (like Mendeleev)
Horizontal Rows= periods (1-7)
Columns= groups- contain elements of the same family (or group) (1-18)
Alkali Metal
Group 1
Have 1 valence electron (want to lose electron)
Shiny, soft metals, highly reactive
Do not occur naturally as free elements
Reactivity increases down the group(as outer electron gets further from nucleus and becomes easier to remove)
By losing electron they become cation and stable
