Flashcards: Measurement Uncertainties and Periodicity — 87 cards

What sections are included in a Grade 11 experimental write-up?

It includes title, summary, theory, apparatus and method, observations, calculations and analysis, uncertainties, conclusion, and extensions.

When can safety goggles be removed during a laboratory activity?

Only after all groups have completed the activity.

What safety equipment must be worn throughout a laboratory activity?

Safety goggles or other required safety equipment.

How should acid and water be mixed safely?

Acid must always be poured into water, never water into acid.

What must never be done with used chemicals in the lab?

Used chemicals must not be returned to storage bottles.

Where should used chemicals be placed after use?

In appropriate waste containers.

What is an element in chemistry?

A pure substance that cannot be broken down by ordinary chemical means.

What defines a compound as a pure substance?

It consists of two or more substances combined and can be decomposed chemically.

What is a mixture in terms of substance combination?

A combination of two or more pure substances retaining their own properties.

What distinguishes a heterogeneous mixture?

It is non-uniform and contains more than one phase.

What is a homogeneous mixture also called?

A solution that is uniform and contains one phase.

What is a physical property?

A property determined without changing a substance's composition.

What does a physical change do to matter's chemical identity?

It leaves the chemical identity and composition unchanged.

What results from a chemical change?

At least one new substance with different composition and properties.

What does the atomic number represent in an atom?

The number of protons in the nucleus.

What is the mass number of an atom?

The total number of protons and neutrons in the nucleus.

What distinguishes isotopes from radioisotopes?

Radioisotopes are radioactive isotopes.

How are isotopes defined?

Atoms of the same element with different neutron numbers.

What is average atomic mass?

The weighted average of all naturally occurring isotopes of an element.

What does the formula $AW = \frac{(p_1m_1)+(p_2m_2)+(p_3m_3)+\dots}{100}$ calculate?

The average atomic mass of an element.

In the average atomic mass formula, what does each $p$ represent?

An isotope's percentage abundance.

In the average atomic mass formula, what does each $m$ represent?

An isotope's isotopic mass.

What are significant digits in a measurement?

All digits known with certainty plus one uncertain digit.

Are non-zero digits significant in measurements?

Yes, all non-zero digits are significant.

Are zeros between significant digits significant?

Yes, zeros between significant digits are significant.

Are leading zeros used only to locate the decimal point significant?

No, leading zeros used only to locate the decimal point are not significant.

How many decimal places should the result have in addition or subtraction?

The same number as the quantity with the fewest decimal places.

How many significant digits should the result have in multiplication or division?

The same number as the quantity with the fewest significant digits.

How is a number expressed in scientific notation regarding digits before the decimal?

With one digit before the decimal point.

Are all digits in the first factor of scientific notation significant?

Yes, every digit in the first factor is significant.

What is absolute uncertainty in measurement?

It is the uncertainty measured directly in the same unit as the quantity.

What is the usual uncertainty for a direct scale measurement?

It is generally half the smallest scale division.

How is percentage uncertainty calculated?

By dividing absolute uncertainty by measured value and multiplying by 100%.

What happens to absolute uncertainties when values are added or subtracted?

Their absolute uncertainties are added.

How are uncertainties combined when values are multiplied or divided?

Their percentage uncertainties are added and converted back to absolute uncertainty.

When are two measurements considered equal regarding uncertainties?

When their deviation is less than the combined uncertainties of both.

What is the uncertainty of a ruler calibrated in millimetres?

± 0.5 mm

What formula gives uncertainty in the average from several measurements?

$u=\frac{\mathrm{maximum}-\mathrm{minimum}}{2}$

What is the average and uncertainty for measurements 5.0, 4.8, 5.3, and 4.9?

5.0 ± 0.25

What are absolute uncertainties?

Uncertainties measured directly in the unit of the quantity.

How do you combine uncertainties when adding or subtracting measurements?

Add their absolute uncertainties.

What is the sum of (6.2 ± 0.1) and (3.4 ± 0.2) including uncertainty?

9.6 ± 0.3

What is the difference of (6.2 ± 0.1) and (3.4 ± 0.2) including uncertainty?

2.8 ± 0.3

How do you combine uncertainties when multiplying or dividing measurements?

Add their percentage uncertainties.

What is the product of (4.0 ± 0.2) and (2.0 ± 0.2) with uncertainty as a percentage?

8.0 ± 15%

What is the product of (4.0 ± 0.2) and (2.0 ± 0.2) with uncertainty as an absolute value?

8.0 ± 1.2

What determines the number of digits retained in a final calculated answer?

The least number of digits in any measurement.

Who identified groups of three similar elements called triads in 1829?

Johann Dobereiner

In which year did Johann Dobereiner identify triads?

1829

Who arranged elements by increasing atomic mass and noted properties repeated every eighth element?

John A. R. Newland

In which year did John A. R. Newland observe properties recurring every eighth element?

1864

Who stated that elements arranged by increasing atomic mass show similar properties at regular intervals?

Mendeleev

In which year did Mendeleev propose the periodicity of element properties by atomic mass?

1869

What is a group or family in the periodic table?

A vertical column of elements with similar properties

What is a period in the periodic table?

A horizontal row of elements

What are valence electrons?

Electrons in the highest occupied energy level of an atom.

Which metals are in Family IA?

Alkali metals.

How many valence electrons do alkali metals have?

One valence electron.

What gas do alkali metals form when reacting with water?

Hydrogen gas.

What is the reactivity of noble gases in Family 0 or VIII?

They generally do not react and have very stable atoms.

How many valence electrons do noble gases have, except helium?

Eight valence electrons.

What is an ion?

An atom or group of atoms with a charge from gained or lost electrons.

What holds oppositely charged ions together in ionic compounds?

Electrostatic attraction.

What is a periodic trend in the periodic table?

A gradual and consistent change in properties within periods or groups.

What does atomic radius measure in an atom?

The distance from the nucleus to the outermost electron's most probable location.

Why does atomic radius increase down a family?

Because the number of energy levels and shielding increase.

Why does atomic radius decrease across a period?

Because nuclear charge increases while energy levels stay the same.

What is ionization energy?

The energy required to remove an electron from an atom.

How does ionization energy change down a family and across a period?

It decreases down a family and increases from left to right across a period.

What is electronegativity?

The overall tendency of an atom to attract an electron.

How does electronegativity relate to an element's tendency to gain electrons?

Greater electronegativity means a greater tendency to gain electrons.

What distinguishes ionic bonding from covalent bonding?

Ionic bonding transfers electrons from metal to nonmetal, covalent shares electron pairs between nonmetals.

What defines a single covalent bond?

Two atoms sharing one pair of electrons.

What is bonding capacity in chemistry?

The number of electrons lost, gained, or shared by an atom when bonding.

How does electronegativity difference affect bond polarity?

Greater difference makes the covalent bond more polar.

What electronegativity difference indicates an ionic bond?

A difference greater than 1.7.

What does VSEPR theory state about electron pairs?

Electron pairs repel and occupy positions as far apart as possible.

What are the shapes and bond angles for two, three, and four electron pairs?

Linear 180°, trigonal planar 120°, tetrahedral 109.5°.

What shape does ammonia have and why?

Trigonal pyramidal due to one lone pair repelling three shared pairs in a tetrahedral arrangement.

What is the most probable arrangement of two electron pairs around a central atom?

Linear

What is the most probable arrangement of three electron pairs around a central atom?

Trigonal planar

What is the most probable arrangement of four electron pairs around a central atom?

Tetrahedral

What is the ideal angle between orbitals in a linear arrangement?

180°

What is the ideal angle between orbitals in a trigonal planar arrangement?

120°

What is the ideal angle between orbitals in a tetrahedral arrangement?

109.5°

According to VSEPR theory, how are the four shared electron pairs in methane arranged?

Tetrahedrally around carbon

What is the experimentally observed bond angle in methane, CH₄?

109.5°