Isotopes Beta Decay Atomic Weight Basic Chemistry

Front 1

atoms that have the same number of protons and electrons but different number of neutrons in the nuclei are called -?

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Isotopes

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Because isotopes of an element have different numbers of neutrons, they also have different ____?

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mass numbers

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isotopes are chemically like because ______?

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they have identical numbers of protons and electrons

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Amore precise measure of the mass of one isotope relative to another is known as the _______?

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isotopic mass

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Isotopic mass determined by comparison to a standard 12C which is defined having a mass of exactly 12 atomic mass units (amu)

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12C (carbon 12)

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1 amu =

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1 amu = 1/12 the mass of a 12C atom

Example: isotopic mass of 10B=10.013 amu
Isotopic mass of 11B=11.009 amu

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Since boron as well as most other elements is found in nature as a mixture of isotope. So from this example the ATOMIC WEIGHT of the 2 isotopes of B is obtained from the weighted average of the isotopic masses of B present in nature
t or f

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TRUE

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Atomic weight: of an element is a weighted average mass of the atom in naturally occurring sample of the element. A weighted average mass reflects the mass and the relative abundance of the isotopes as they occur in nature.
T OR F

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TRUE

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Calculating the ATOMIC MASS of an element; you must know:
1
2
3

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A) the number of stable isotopes of that element
B) the mass of each isotope
C) the natural percent abundance of each isotope

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Can an atom have just any number of neutrons?

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Atoms with a few too many neutrons can sometimes exist for a while, but they are unstable

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Light elements tend to have 1. __ __ ___ ____as protons; heavy elements 2. ____ ____ ______ ____ in order to stick together

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1. about as many neutrons
2. need more neutrons than protons

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Unstable atoms are radioactive; their nuclei change or decay by spitting out radiation, in the form of ____ __ ________ ?

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particles or electromagnetic waves.

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When 3H metamorphoses into helium 3, it also gives off an electron – which hardly has any mass, and its endowed with a negative charge that exactly cancels one proton. This process is known as 1. ____ _____ , and the electron is called a 2. ____ ______.

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1. Beta Decay
2. beta particle.

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What happens when an atom doesn’t have enough neutrons to be stable?

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Protons turns into a neutron
That’s the case with beryllium 7, 7Be4 it decays to lithium 7….

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Nuclear reaction looks like this:

7Be4 => 7Li3 + 0e1
name the elements starts as ____ becomes _____?

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beryllium 7, 7Be4
it decays to lithium 7…. 7Li3 + 0e1

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Third type of radioactive emission is

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gamma decay. After alpha or beta decay, a nucleus is often left in an excited state-with some extra energy. It then calms down by releasing this energy in the form of a very high frequency photon, or electro magnetic wave, known as gamma ray.

Front 17

- n => p + e-
This is the formula for what

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a beta decay. What you’ve got is a neutron decaying into a proton and an electron:
“Mass Conservation” has to take energy into account. If you add up all the mass and energy before and after a nuclear reaction, the same totals come out.

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Half-life is

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is the amount of time it takes for half of the atoms in a sample to decay. The half-life for a given isotope is always the same. It doesn’t depend on how many atoms you have or on how long they have been sitting around

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The half-life is always the same, but

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the half gets smaller and smaller.

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Valence:

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Valence: is the tendency of elements to form compounds

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Valence number:

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Valence number: is a number indicating a charge on an ion or the number of pairs of electrons shared by one element with another. It is the bonding in a compound
Most elements exhibit a variety of valence numbers depending upon the particular compound they happened to be a part of.

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To determine the valence number of an element in a compound...

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1) elements of group I of the periodic table have a valence number of 1+
2) elements of group II have a valence number of 2+
3) elements of group VII have a valence number of -1 (7-8=-1)
4)elements of group VIA have a valence number of 2- (6-8=-2)
5)elements of group VA have a valence number of -3 (5-8)=-3
6)elements of group IVA (non-metals) and group VIIIA (nobel gases) usually do not form ions, usually C Si are found in molecular compounds

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elements of group I of the periodic table have a valence number of __

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1+

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elements of group II have a valence number of

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2+

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3) elements of group VII have a valence number of
4)elements of group VIA have a valence number of
5)elements of group VA have a valence number of
6)elements of group IVA (non-metals) and group VIIIA (nobel gases)

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3. -1 (7-8=-1)
4. 2- (6-8=-2)
5. -3 (5-8)=-3
6. usually do not form ions, usually C Si are found in molecular compounds

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A homogeneous mixture has

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the same uniform appearance and composition throughout. Many homogeneous mixtures are commonly referred to as solutions.

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A heterogeneous mixture consists of

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visibly different substances or phases. The three phases or states of matter are gas, liquid, and solid.

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A MIXTURE is

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a combination of two or more substances that are not chemically united and do not exist in fixed proportions to each other. Most natural substances are mixtures.

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A mixture can be physically separated into

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pure compounds or elements.

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A pure compound has

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a constant composition with fixed ratios of elements.

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The compounds may be divided into two groups. Those molecules that consist of charged ions with opposite charges are called

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IONIC. These ionic compounds are generally solids with high melting points and conduct electrical current.

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The other type of molecules are called 1. _____ and do not consist of ions.

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1. COVALENT

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Which type of compounds have low melting points and do not conduct electric current.

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Covalent

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COMPOUNDS contain

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two or more different elements in a chemically combined form.

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The simplest form of most matter, other than simple elements which still retains specific properties, is in the form of compounds. The simplest form of a compound is a

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molecule.

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A MOLECULE contains

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two or more atoms.

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When an element consists of two identical atoms it is called a ________ molecule.

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DIATOMIC