Chapter 2 Flashcards
Symbol
The abbreviation for an element consisting of a capital letter (may also be followed by a lower letter)
Formulas
A combination of symbols, subscripts, and possible superscripts that identifies the composition of an element, compound, or ion
Why are symbols combined?
Chemists write chemical symbols together in chemical formulas to identify compounds
What do formulas tell about each element?
Formulas give the relative number of each type of element in a compound
Subscripts
In chemical formulas to indicate the relative proportions of the elements present
What letters are capitalized in a symbol?
The first letter in a symbol is the only letter to be capitalized
Do all symbols start with the same letter as the English name?
No
How are compounds represented?
Compounds are represented by the combination of chemical symbols in chemical formulas
The law of conservation of mass
During a chemical reaction mass is neither gained nor destroyed
Explain the law of conservation of mass
- During a chemical reaction mass is neither gained nor destroyed
- it is converted into different states of matter but not lost or gained
What are the two laws the conservation of mass lead to?
- Law of definite proportions (law of constant composition)
- Law of multiple proportions
Law of definite proportions
The composition of a compound is fixed
Proportion
the ratio of the number of a certain item divided by the total number of items (compare to percent)
What is the proportion of mass in a compound?
The proportion of mass of an element in a compound is the ratio of the element to the total mass of the compound
Percent
The amount of a certain component in 100 units of the atom
What is the percent by mass of an element?
The percent by mass of the element in the compound Is just the proportion of the element multiplied by 100
The law of multiple proportions
Two or more elements combine to form more than one compound, for a fixed mass of one element, the masses of each of the other elements in the compounds occur in a small whole-number ratio
What led to the development of the law of conversation of mass?
Careful measurement of the masses of reactant and products in chemical reactions led to the development of the laws of conservation of mass, definite proportions, and multiple proportions
Why are the three laws important?
The three laws of chemical composition formed the basis for the theoretical development of chemistry
Daltons Atomic Theory
The theory that matter is mate up of small particles that have properties characteristic of an element
Dalton’s atomic theory hypothesis
- Matter is made up of tiny, indivisible particles called atoms
- Each atom of a particular element has the same mass but the mass of an atom of one element is different from the mass of an atom of any other element
- Atoms combine to form what we now call molecules. When they do so, they combine in small whole number ratios
- Atoms of some pairs of elements can combine with each other in different small whole-number ratios to form different compounds
Atoms
A single particle of any elements - the smallest possible amount of an element that retains the properties of that element
Molecules
An uncharges, covalently bonded group of atoms
What three things did Dalton’s atomic theory explain
- The law of conservation of mass
- The law of definite proportions
- The law of multiple proportions
Cathode rays
A beam of electrons
How were electrons discovered?
- Constructed a cathode rube and observed how a beam of particles known as a cathode ray passed through the tube
- discovered they have a negative charge because they bent away from a magnet
- cathode rays move in straight lines
- have a charge to mass ratio of -1.76x10^8 C/g (coulomb)
Electrons
A negatively charged subatomic particle found outside the nucleus, a fundamental particle of nature
Charge of an electron
-1.60x10-19 C
Mass of an electron
9.10x10^-28
Radioactivity
the emission of particles during nuclear decay
Three types of radioactivity
- Alpha
- Gamma
- Beta`
Rutherfords Model
- The atom has a positive charge and the majority of its mass are located in a relatively small area, which he later names the nucleus
- the majority of the atom is empty space. Small, negatively charged electrons are spread throughout this empty space
- The number of negatively charged electrons is equal to the number of positively charged protons inside the nucleus
Nucleus
The center of the atom, consisting of the protons and neutrons. It accounts for almost all of the mass, but almost none of the volume of an atom
Proton
A subatomic particle found in the nucleus with a mass slightly greater than 1u and a charge of +1
Neutrons
A subatomic particle sound in the nucleus that has no charge and a mass slightly greater than 1u
Charges on PNE
proton = +1
Electron = -1
Neutron = no charge
Why is daltons atomic theory important?
Daltons atomic theory was an explination for why the three laws of chemical combination worked, and it provided the theoretical background for the entire future development of chemistry
How were the atom’s parts found?
Experiments demonstrated that the atom is not indivisible but consists of a nucleus made up of protons and neutrons that us surrounded by a cloud of electrons
Explain the charges on an atom
The charges on protons and electrons are equal in magnitude and atoms are electrically neutral so atoms contain equal numbers of protons and electrons