Chapter 4 Chemistry test
Order by
90 terms
Terms | Definitions |
|---|---|
 Democritus | ancient greek thinker believed that matter could be divided into smaller and smaller perticles until a basic particle was reached. He was the first to suggest the existence of atoms |
| atoms | the smallest particle of an element that retains both the chemical and physical properties of that element |
| John Dalton | performed experiments to arrive at his Atomic Theory |
| John Dalton's Atomic theory | 1. All matter is composed of extremely small particles called atoms 2. Atoms of the same element are identical. Atoms of different elements are different 3. Atoms cannot be subdivided, created, or destroyed. 4. Atoms of different elements can combine in simple, whole-number ratios to form compounds 5. in chemical reactions, atoms are combined, separated or rearanged |
| Law of multiple proportions | Atoms of different elements can combine in simple, whole-number ratios to form compounds |
| Why isn't all of Dalton's theory true? | Atoms can be broken down and atoms of the same element are not identical because isotopes of that element exist |
| Atoms are made up of | protons, neutrons, and electrons |
| actual mass of protons and neutrons | 1.67x10^-24 grams |
| Chemists use _______ comparisons of the masses of atoms | relative |
| the unit of comparison is the | atomic mass unit (amu) |
| Atomic mass unit | defined as 1/12 the mass of a carbon atom that contains six protons and six neutrons |
| For all practicle purposes the mass of a single proton or neutron is | 1 amu |
| symbol of electron | e- |
| relative electrical charge of electron | 1- |
| Approximate relative mass (amu) of electron | 1/1840 |
| Actual mass of electron | 9.11x10^-28 |
| symbol of proton | p+ |
| Relative electricalcharge of proton | 1+ |
| approximate relative mass of proton | 1 |
| actual mass of proton | 1.67x10^-24 grams |
| symbol for neutron | n^0 |
| relative electrical charge for neutron | 0 |
| approximate relative mass for nuetron | 1 |
| actual mass | 1.67x10^-24 grams |
| John Dalton's model of the atom | atom was invisible and the smallest particle that could exist |
| Approximately 50 years after John Dalton's death, the idea of the invisible atom was shattered after the discovery of | protons, neutrons and electrons |
| Joseph J. Thomson discovered... | the electron |
| Joseph J. Thomson proposed a model of the atom referred to as the... | "plum pudding model" |
| plum pudding model | has negatively charged electrons (raisins) embedded into a lump of positively charged protons (the dough) |
| The discovery of the electron led to two hypotheses: | -since atoms are neutral, they must contain something positively charged -since electrons weigh so little, atoms must contain something that accounts for the mass |
| Robert Milikan | figured out the mass of the electron during his Oil Drop Experiment |
| Ernest Rutherford | discovered the nucleus of an atom in his "Gold Foil Experiment" |
| gold foil experiment | Rutherford aimed a beam of alpha particles at a piece of gold foil surrounded by a flouresent screen. most of the particles passed through the foil. a few particles were deflected. |
| Rutherford concluded that | most of the alpha particles pass through the gold foil because the mass and positive charge is concentrated in a small region of the atom. He called this region the NUCLEUS. particles that pass near or approach thenucleus are deflected |
| Niels Bohr | -proposed a model of the atom where electrons orbit around the nucleus -the electrons in a particular orbital have fixed energy and do not lose energy and fall into the nucleus |
| Bohr's model was referred to as the | "Planetary model" |
| The rungs of a ladder are analogous to the energy levels in an atom. | The higher the energy level occupied by the electron, the more energetic it usually is from the nucleus |
| amount of energy lost or gained by every electron is | not always the same |
| unlike the rungs of a ladder... | the energy levels in an atom are not equally spaced |
| quantum of energy | the amount of energy required to move an electron from its present energy level to the next higher one |
| Erwin Schrodinger | used the new quantum theory to write and solve a mathmatical equation describing the location and energy of an electron in a hydrogen atom |
| quantum mechanical model | -proposed by Erwin Schrodinger, it is a modern description of electrons in atoms -does not define the exact path of an electron but is concerned with the likelihood of finding an electron in a certain region of space sround the nucleus |
| today we use the | Quantum Mechanical model |
| Atomic number | number of protons in the nucleus of an atom |
| Mass number | number of protons + number of neutrons |
| since an atom is neutral... | number of protons = number of electrons |
| number of protons determines... | what the atom is |
| Atoms of the same element will always have the same number of ________ and _________ | protons, electrons |
| atoms of the same element can have a different number of _____________, and therefore, a different _____________ | neutrons; mass number |
| Isotopes | atoms of the same element that have different numbers of neutrons and a different mass number |
| to distinguish atoms, we use... | chemical symbols |
| 1 H 1 | top 1: mass number bottom 1: atomic number H: element symbol |
| hyphen notation | name of the element-mass number |
| determine number of protons | bottom left number |
| determine number of electrons | same as protons |
| determine number of neutrons | mass number-atomic number (top-bottom) |
| alpha | consists of the nuclei that have been emitted from a radioactive source |
| alpha particles | contain 2 protons and 2 neutrons |
| Because of their large mass and charge, alpha particles | do not travel very far and are not very penetrating. |
| Alpha particles are easily stopped by | a sheet of paper or dead skin cells on the surface of your skin |
| Alpha particles are dangerous when injested because... | they can penetrate soft tissue |
| Beta | consists of fast moving electrons formed by the decomposition of a neutron |
| Beta particles are ___________ than alpha particles and have ________________ | much smaller; 1/2 as much charge |
| Beta particles are | more penetrating than alpha particles |
| Beta particles can be stopped by | aluminum foil or thin pieces of wood |
| Gamma | consists of electromagnetic energy |
| Gamma particles are very _____________ and can only be stopped by.... | penetrating; several feet of concrete or several inches of lead |
| nuclear stability-- the stability of a nucleus depends on... | its proton to neutron ratio |
| For elements of low atomic number, below about 20, this ratio is _________. This means the nuclei have equal numbers of ___________ | one; protons and neutrons |
| Above atomic number 20, the stable nuclei have more ____________ than ____________ | neutrons; protons |
| band of stability | contains all stable nuclei |
| neutron/proton ratio=1.0 | stable ratio for lighter isotopes |
| neutron/proton ratio=1.5 | stable ratio for heavier isotopes |
| Region A | unstable nuclei undergo beta decay |
| Region B | unstable nuclei convert a proton to a neutron |
| Region c | unstable nuclei undergo beta decay |
| Half-life | the time it takes for half of the nuclei in a radioactive sample to decay |
| Stability is indicated by its half-life. the longer the half-life... | the more stable the radioisotope |
| Chemical Reaction | -atoms separate or combine without any changes to the nucleus -only electrons are involved -new compounds are formed |
| Nuclear Reation | -nucleus changes in composition -new elements are formed by 2 processes: Fusion and Fission |
| Fusion | two nuclei combine to form a new nucleus |
| Fusion occurs on the ________ with _____________ combining to form ____________ | sun; 2 hydrogens; helium |
| Fission | nucleus decays, releasing radiation |
| electron purpose | determines the chemical properties of a substance |
| proton purpose | determines the identity of the substance |
| neutron purpose | provides nuclear stability, they are "glue" |
| Elements 1-20 have atoms that are stable when... | the number of protons and neutrons is approximately equal |
| Elements above 20 need... | increasingly more neutrons than protons to be stable |
| Elements above 83... | can't be stable and are radioactive |
| the strong nuclear force | the force that holds the nucleus together and does not allow the protons to fly apart due to repulsion |
First Time Here?
Welcome to Quizlet, a fun, free place to study. Try these flashcards, find others to study, or make your own.