Key Concepts of Chemistry Flashcards
What was John Dalton’s theory (1803)?
He published his own three-part atomic theory:
1. All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed.
2. Atoms of the same element are exactly alike, and atoms of different elements are different.
3. Atoms join with other atoms to make new substances.
Much of Dalton’s theory was correct, but some of it was later proven incorrect and revised as scientists learned more about atoms.
What was J.J Thomson’s model (1897)?
Used a cathode-ray tube to conduct an experiment
This discovery identified an error in Dalton’s atomic theory. Atoms can be divided into smaller parts.
Because the beam moved away from the negatively charged plate and toward the positively charged plate, Thomson knew that the particles must have a negative charge.
Thomson proposed a model of an atom called the “plum-pudding” model, in which negative electrons are scattered throughout soft blobs of positively charged material.
What was Ernest Rutherford’s model (1909) ?
Rutherford developed a new model which said that most of the atom’s mass is found in a region in the centre called the nucleus.
In Rutherford’s model the atom is mostly empty space, and the electrons travel in random paths around the nucleus.
What was Ernest Rutherford’s experiment?
He shot a beam of positively charged particles into a sheet of gold foil.
Most of the particles did continue in a straight line (as you would expect from plum pudding model). However, some of the particles were deflected to the sides a bit, and a few bounced straight back.
What is the relative charge and relative mass of protons, neutrons and electrons?
Particle: Relative Charge: Relative Mass
Protons: +1: 1
Neutrons: 0: 1
Electrons: -1: 1/1836
Why do atoms contain equal number of protons and electrons?
Atoms are neutral and the charges on a proton are +1 and on an electron are -1, therefore amount of protons = amount of electrons, so that the charges cancel.
Describe the term “isotope”
Atoms of the same element that have the same number of protons but different number of neutrons.
How did Mendeleev arrange the elements, known at that time, in the periodic table?
He ordered his table in order of atomic mass, and left gaps for elements that he thought had not been discovered yet.
How did Mendeleev use his table to predict the existence and properties of some elements not then discovered?
Mendeleev realised elements with similar properties belonged in the same groups in the periodic table and so was able to leave gaps and place the discovered elements where they fit best. Elements with properties predicted by Mendeleev were later discovered and filled the gap.
What is the meaning of atomic number of an element in terms of position in the periodic table and number of protons in the nucleus?
Elements are arranged in order of atomic (proton) number (bottom number) and so that elements with similar properties are in columns, known as groups.
Elements in the same group have the same amount of electrons in their outer shell, which gives them similar chemical properties.
What does the endings –ide and –ate in the names of compounds mean?
These endings are used for the negatively charged ions in a compound.
-ide means the compound contains 2 elements.
-ate means the compound contains at least 3 elements, one of which is oxygen
Describe the term “ionic bonding”
Transfer of electrons between a metal and non-metal.
Why do ionic compounds have a high melting point?
They have a lattice held together by strong electrostatic forces of attraction between oppositely charged ions. Therefore, lots of energy is needed to break these bonds.
Can ionic compounds conduct electricity?
Ionic compounds can conduct electricity when molten or in solution, but not as solids as ions aren’t free to move.
Describe the term “covalent bonding”
A sharing of a pair of electrons between non metals.
